Yearly Archives: 2017

Back in November I covered a repair to a Southerly that had been T-boned.
Well the job was finished and I was just tidying up when the owner asked me to see if I could locate his fluxgate compass.
I stuck my head in various lockers and other likely places it might have been fitted.
This 1999 boat is in very good order, all the varnish, trim, flooring and upholstery looking like is on a boat a couple of years old, so I really wasn’t looking for trouble.

The following shots were taken after I’d finished the job but they could have equally been taken before I started.

When I checked under the raised seating area I noticed that the gelcoat wash that had been put on the plywood bulkheads had cracked in a couple of places.
I poked one of these marks with my finger and I was frankly astonished that my finger went right through the plywood.
Under this raised seating area is long length of plywood that stretches from the water tank, in front of the galley area, to the main lateral bulkhead splitting the saloon from the forward cabin.
Off this longitudinal bulkhead there are two sheathed  plywood  locker sides and also the two port side chain plate knees.
It appears that when the builder fitted this plywood structure, they simply butted each section of plywood together, before glassing it in place and then sheathing it.
However in a couple of places, on the less important locker sides, they didn’t sheath the panels entirely, leaving an area around 4″ by 12″ in the middle of the panel that just had a coating of gelcoat.

I poked a little more at the forward locker side and it was found to be water logged mush, though strangely no smell at all.
With a multitool I cut out the glass tabling around the panel and scooped out all the soaked rotten wood.
I then turned my attention to the longitudinal bulkhead and this was slightly dryer but was still wet and crumbled in my hand.
I followed this process gradually working my way round the structure removing all the rotten wood.

Things got a bit more serious when looking at the main chainplate knees.
Whilst from the outside the knees looked fine, if you look at the photo carefully you can see the bolts are at a slight angle.
In fact four or five of the nuts were only finger tight.
With the chainplate bolts removed we could inspect the backing plate, which surprised us as it was made from aluminum plate rather than 316 Stainless.
All the holes had elongated showing that the plate had raised under load by around 30mm.
Using a hole cutter I drilled out an exploratory 30mm hole through the sheathing to check the Knee core and found nothing but damp dust.
After cutting away the side of the knee it was obvious that the knees would need rebuilding and also the realization that the rig could have come down at any time.

We had established that the rot had not effected the main forward lateral bulkhead though given a few more months then this could have been an issue as well.
To inspect further aft we needed to remove the stainless water tank.
In this Southerly this was no mean feat as access to the outlet from the tank is extremely difficult.
How the builder thought is was a good idea to place the outlet on the aft side of the tank, under the galley, is beyond me, especially as the factory fitted calorifier, fridge compressor and associated pipework would all have to be removed to gain any kind of reasonable access to the single jubilee clip securing the outlet water pipe.
In the end after three hours of knuckle grazing effort we managed to get a modified spanner on the tank fitting and with an 1/8 of a turn at a time wound the whole fitting out of the tank.
Removal of the tank was then pretty straight forward although we did notice there was no inspection hatch or obvious way to clean the tank.
So we decided to get the tank modified, blanking the original outlet and fitting a new one on the forward side which would have much easier access and also to fit an inspection hatch.
With the tank removed we could continue the rot chase and with relief it was found not to have continued into any of the galley supporting structure and bulkheads.
The aft chainplate knee however was found to be rotten and had twisted its position almost as much as the main chainplate knee and the water tank locker side would have to be replaced.

It was by now obvious that over time,  the connected sheathed plywood sections had rotted due to moisture getting sucked in by capillary action.
However even though we strongly suspected the bottom inside corner of the forward locker to be the initial entry point I couldn’t find any definitive proof.
With this in mind I wasn’t keen to simply replace the wood for the fear of the same problem recurring in future.
Given the excellent condition of the rest of the interior I also needed a solution that didn’t require disassembly of the entire saloon seating area.
So I decided to replace all the panels except for the knees, using a 10mm thick plastic honeycomb core, called Nidaplast, which would then have two layers of 250 gram chopped strand matt laminated to each side.
The resulting panel is stiffer and lighter than plywood , with the obvious additional benefit of there being nothing to rot in the future.
The chainplate knees however would be 25mm marine plywood, due to the compression of the chain plate bolts. The knees would be glassed to the hull and sheaved individually.

I find the easiest way to template an awkward shape is to use 2″ wide strips of hardboard and stick them together using a hot glue gun.
The resulting shape can then be transferred over to the sheet material you wish to use, marked up and cut out.

When I removed the old rotten wood I removed one side of the sheathing only.
The remaining sheathing side was cleaned and keyed so that it would provide a solid location for the new knee.
The new plywood was given a coat of neat west epoxy and then a thickened mix using 406 colloidal silica was liberally applied to the side of the old sheathing.
The new panel was inserted and clamped into position.
Using a large syringe more epoxy/406 mix was injected into the joints between the knee and the hull.
Then using a tongue depressor an epoxy fillet was created round the edges.

24 hours later the epoxy has set and the clamps can be removed.
The surrounding area can then be cleaned, removing al traces of stray epoxy apart from the fillet and the hull was vigorously keyed using a grinder with a flap disc ready for the knee to be laminated to the hull and then sheathed.
Grinding and sanding old grp is a horrible, messy process, generating a huge amount of fine dust that gets everywhere.
Using a sander with dust extraction is another method but it takes at least three times as long, so I take some time and sheet off the local area, don disposable overalls, mask and goggles, take a deep breath and get stuck in.

Once the dust generating process has finished the sheeting can be removed and everything is given a through vac down to remove all traces of dust.
The glass cloth can now be cut out ready for laminating.
Do not be tempted to do this during the laminating process as what can be a messy process at the best of times can quickly turn into a nightmare.
I used a mixture of cloths.
Firstly 250g chopped strand mat.
This in my view provides a better initial key to the hull and bare wood than woven cloth.
Followed by 300g biaxial woven cloth, which smooths everything out, it falls to shape well and wets out very easily.
The main strength is provided using overlapped layers of 150mm wide 450g biaxial cloth tape.
Whilst this tape is thick and quite heavy it falls into place well and there is usually enough residual resin in the previous layers to wet it out using a roller.

I think I’ve pointed out before in earlier articles that its important not to use too much resin.
Any fool can wet out layers of chopped strand mat by flooding it with resin but this results in a weak, brittle and potentially dangerous layup.
Use the resin sparingly and work it in with the brush and roller.
It takes time and patience done correctly, around a full working day to fully laminate a knee in this case.
If it was any faster then I’d be concerned that the layup was resin rich.

With the structural knees completed, work can move onto rebuilding the locker sides and the under floor support structure.
The manufacture of the grp honeycomb panels is a straight forward process and is ideally carried out on a large bench.
Templates were made for each panel using the harboard strips and glue gun as before.
These were then transferred over to the nidaplast board, which in turn were used for patterns to cut out  four layers of 250g csm for each panel.
Laying up on a bench is so much easier and much faster so that two layers were applied to one side of the nidaplast before lunch and keeping the temperature up using heat lamps the other side was laminated in the afternoon.
On the inner side of a couple of the locker sides I also applied a layer of tight woven 180g cloth which results in a very smooth surface, which is much nicer than the usual csm finish.

Once the honeycomb panels have been trimmed they were all dry fitted to ensure they were the correct size and to establish the order each panel would have to be laminated.
Each panel would have to be laminated around all four edges, on both sides and the only available access was through the locker tops, which resulted in a specific order.
All the panels were made using polyester resin and so I used polyester bonding paste to essentially stick the panels in place.
This bonding paste is fast acting and easy if a little messy to use.
It’s also used for most modern yachts these days to bond the deck to the hull, so its very strong but can be brittle and doesn’t allow flex.
I used four layers of 100mm wide tape for each joint.

The rebuild almost complete the next job was to give all the panels three coats of gelcoat.
The original colour was bilge grey but in practice we find white is a lot more user friendly, especially when trying to find stuff deep in the bottom of a locker at a later date.
The first two coats were standard white gelcoat and applied using a 3″ brush and the third coat had wax with styrene added so the finish would be non sticky.
24hours later the gel coat was hard enough for us to refit the modified water tank.

The chain plates were then re fitted using new 316 stainless backing plates and new M12 shouldered stainless bolts with nylock nuts.
The old chainplate bolts were machine screws and threaded all the way which is not good practice as water can draw up through the thread and rot the inside of the knee and also if there is any movement the thread can cut the hole sides like a hacksaw.
The transducer cables were re routed and all the keel bolts given a once over whilst we were there.

This job was a real eye opener to me.
Normally you get a clue or two once stepping on board on whether there is a likelihood to be any rot about.
There’s a kind of smell, an aura, a general feeling that something ain’t right.
However in this case it was a total surprise, given how immaculate and well looked after the boat appeared to be.
Still not found the fluxgate compass and I’m not at all sure how keen the customer is for me to keep looking!

All back together and looking the same as it did when I started.

A significant proportion of our work at the yard comes to us via insurance companies and usually as a result of some unfortunate accident.
In this particular case a Southerly 115 was clobbered whilst sitting on her mooring by 40′ yacht who were obviously having a few handling issues.
Southerly’s of this era are pretty heavily built, so to have an impact where the teak rubbing strake was shattered, hull and deck punctured and the internal bulkhead pushed to port, shearing the headlining screws, separating the grp lining from the coach roof and companionway, it must have been a hell of a bang.

In point of fact the hull was fine as the hull deck joint is under the teak rubbing strake, some 20″ below the side deck level.
The vertical section of deck is around 10mm thick and the horizontal is made up of a 5mm inner layer, 12mm plywood as a core and another 8mm of glass and gelcoat on top.
There is also a grp and gelcoated toe rail which was integral to the deck, having been molded when the boat was built.

Grp is strong, flexible and can take a lot of abuse without much visible evidence.
Gelcoat however is not very flexible and will crack and craze very easily after an impact.
So if you can see the damage is right down to the laminate you just know the gelcoat damage will be far worse and will possibly spread over time.

A common misconception is that those nasty little cracks and crazes in the gel coat do not emanate from the surface down, in fact the opposite is usually true.
An impact makes the grp flex, the gelcoat attached to it can’t flex as much, so it cracks from the laminate outwards.
So the only way of successfully repairing gel cracks is to grind all the way back to the laminate and re gel.

In this case one of the first jobs was to trace all the cracks and crazing caused be the collision.
I employ young eyes for this task as even with my reading glasses on it’s easy to miss tracking a crack a fraction of a millimeter wide.
All the crack extremities are marked with a black marker pen to give a guide to the area needing work and everything inside the marks is ground away.

Before we grind however, an area within the damaged area is sanded with 1000 grit wet and dry and then cut with a cutting compound before buffing to a high polish.
A 50mm square section is then cut out which will be used to get a gelcoat colour match.
To achieve an invisible repair this matching process is possibly the most important.
The gelcoat number from the manufacturer can help but once the boat is over five years old it pays to mix your own as UV light will have effected the original colour.
Looking at this job I estimated that I’d need around 2 to 3 litres of gelcoat.

All the damaged gelcoat was ground away using a flap wheel on a 4″ grinder.
Any evidence of damaged laminate was also ground away, tapering at the edges but ensuring I left a thin laminate so there was something for the new glass to go up against.

The crushed plywood core was cut away and all the jagged edges removed.

Its only at this stage, once all the bad stuff has been removed, that you can take a step back and come up with a rebuilding plan.
The choices really being repair from outside-in, inside-out or start in the middle.
I decided to firstly repair the deck core and then glass outside and then inside.

The plywood core was rebated by 30mm using a trusty multi tool, power file and various chisels.
A 12mm thick plywood infill section was made and dry fitted a number of times to get an exact fit.
The edges of the original deck core and the infill were sealed with neat West epoxy before being glued into position using a West epoxy/colloidal mix.
A 4mm vertical section of ply was also glued into place with epoxy to fill the gap and provide something to glass against.

It was very important to ensure that this was a clean bond and to ensure that there wouldn’t be any exposed epoxy either on the glass or plywood.
The reason for this is that polyester resin in not a good glue so for this job we use epoxy.
Trouble is Gelcoat is polyester based so the repair laminating will be using polyester resin.
The two are not great together so keep them separated.

Epoxy guru’s tell me that I can indeed use Polyester gel coat with epoxy but in this case I’m sticking with polyester.
Laminating with epoxy is a lot more time consuming with much longer curing times not to mention two or three times more expensive.

The laminating process is pretty straight forward.
Wetting out the repair area first before laying on a layer of 450g chopped strand mat (csm).
I always tend to use csm for the initial layers as you get a stronger bond.
In this case I applied three layers of csm, ensuring each layer was well rolled and consolidated which in turn uses much less resin and will result in a stronger laminate.
Remember, resin rich layups are always more brittle and less strong, so be frugal with the amount of resin you use but at the same time ensure every fiber is whetted out.

A straight edge will show you where you have highs and lows in the laminate.
I mark these areas with marker pen and then its just a case of adding more localised layers.
Once there’s a good initial flat layup I can start adding a couple of layers of 350g woven biaxial cloth.

There was a lot more scope for additional layers on the inside repair, as this area will be hidden by internal trim.
So I added a number of extra layers of 450g woven tape which will add significant strength to the overall repair.

I use a masking tape border around the repair to avoid splashes and drips of resin landing outside the repair area.
I’ve seen others who need significantly more protection.
I take a lot of care about cleanliness during laminating, especially when using a consolidation roller and later in gel coating.
If you are not careful you can get into an almighty mess and then transfer that mess everywhere, so my top tip here is develop ocd type tendencies when laminating, although there are others who wish I could extend this tendency to other areas of my life.

After a quick trim and sand with 80 grit paper to remove the odd stray fiber it was time to apply the first coats of gelcoat.

The boat was inside our shed No3 and in early September the conditions were such that I could apply at least five or six coats of gel coat in a day.
Avoid the temptation to apply thick coats of gelcoat, which is very possible as gelcoat is much thicker than resin.
The issue is that during both the mixing process and the application you will introduce air bubbles into the mix which, if applied in a thick layer, will not work their way out to the surface.
Later sanding and compounding will expose these tiny bubbles which are impossible to fill.
The remedy to this is to apply multiple, thin layers of gelcoat.
I was getting gel cure times of around 1 hour, so I applied 5 thin coats during the day, followed by a coat with added wax in styrene which was then left to set hard overnight.

Next day the area was sanded with 240 grit paper using a flat foam block.
The initial hills and valleys are easy to spot as the valleys will remain gloss whilst the rest will be matt.
The trick here is to ring each valley with a marker pen and then remove the gloss using 80 grit to provide a good key.
Additional thin layers of gelcoat were then applied to fill the valleys before another coat over the whole area with added wax.

Its much harder to spot the highs and lows at these later stages so I scribble all over the area with a marker before sanding off using finer and finer grades of paper.
I find 240 grit is my rough starter paper.
This is followed by 600 grit, then 1000, 1500 and if I’m feeling enthusiastic I’ll scribble and sand off using 2000 grit wet and dry paper.

The next stage was to create a new toe rail.
For this I decided to take a mold from the opposite port side toe rail.
The port side toe rail was cleaned, compounded, polished and then had four coats of mirror wax applied and finally buffed to a high shine.
The area around the toe rail was taped using resin proof tape to ensure I could easily get wedges under the mould to release it later.
For the mould I used a contrasting dark blue gelcoat.
This is done so that when making the final part you ensure you get a good coverage of gelcoat as if it’s too thin you will be able to see the blue showing through.

Six layers of glass was laminated over the gel coat.
The next day the mould was popped off using wooden wedges, trimmed and internally waxed and polished.
A new toe rail was then laminated, trimmed and offered up.

Possibly the most challenging part of this repair was to reinstate the molded in, non-slip texture on the deck.
A section of foredeck that had both the same pattern angle and roughly the same pitch was selected and the area was thoroughly cleaned, waxed and polished.
This was a lot harder to do than say as the wax tended to fill up the indentations so I used a stiff scrubbing brush over a soft cloth to ensure the wax was removed and polished.

I applied two coats of gelcoat followed by three layers of csm.
This resulted in a flexible mould that would flex to match the slightly different deck profile of the repair.
The mould was trimmed to the exact size and shape of the section of deck I wanted to recreate.
The corresponding area of deck was sanded hard to remove the old moulded grip and provide a good key.

As the non-slip stands up slightly from the surrounding gelcoat I needed to have a practice on a scrap piece of hardboard to judge how much gelcoat I would need as this repair would need to be done in one hit.
I found that a light coat on the deck and on the mould was just about right.
Starting from one end the mould was placed down onto the deck and by using the flex in the mould it was bent to avoid trapping any air as the two surfaces touched together.
A couple of push cramps and a lead weight were enough to hold the mould in position.
Once the gel had set, the mould was carefully peeled off revealing the non slip surface and a sigh of relief.

With the deck repair complete the toe rail needed to be secured to the deck.
I chose to make an internal wedge out of glass and this was bolted and glued to the deck using Sabatack.
In turn the wedge was coated with Saba and the toe rail pushed down over it.
It was just a case of adding a gelcoat fillet around the toe rail to merge it into the deck followed by the usual sanding, marking, sanding, polishing routine.
A final compound with 300 cut Farecla compound and then UV wax and it was time to grab one of the guys in the yard to see if they could spot the repair.
If you have to point out where the repair was made then you know you’ve been successful.

Various shots of the finished repair…….

Grp boats are pretty resilient and after a bit of elbow grease is applied you can normally get a satisfying finish, even on a thirty or forty year old hull.
However there comes a time after years of compounding, polishing and scrubbing, not to mention dirty fenders, lifting slings, oh and the dreaded UV when there is just no way to get that shine back.
One option, if the damage is localised, is to re-gel coat.
However the general condition of this hull, though sound, was deemed to be too far gone to make this viable unless we re gel coated all the topsides.
Indeed if it wasn’t for the fact that we have a superb paint sprayer here I would have been tempted as the process takes only a little longer in man hours and gel coat is cheaper than good quality paint.
With spraying, the time is taken with the preparation, whereas with reapplying gel coat, the time is all in the final sanding and polishing.
We spray a lot of boats here at the yard so for us this was the obvious route for this Moody 31.

The process is quite straight forward if a little time consuming.
The first job is to take lots of photographs from every conceivable angle.
These will provide a reference for the exact position of vinyl stripes, logos and names that all need to be removed and replaced.
The removal of these vinyl decals can often take much longer than you would expect.
The stripes in good condition will simply peel away given a little persuasion with a heat gun or even better a steam gun but where there are nicks or its worn thin other techniques using a mix of white spirit, Stanley blades and wet and dry sandpaper.
Every last trace of adhesive needs to be removed which is why we try to steer clear of aggressive solvents like acetone which dissolves the glue but with a high risk of spreading a thin layer of glue about when wiping clean.

Good lighting and even better eyes are now required to spot all the dings, chips and star crazing so that these can be treated next.
Often the best way is to sand down the entire topsides area using 150grit on a dual action (da) sander, though from this point on you need to employ very good dust extraction.
Dust is the make it or break it of a good spray job so we use  dust extractors on each da and wash down at least twice a day.
Also the deck and lower hull is taped up with a mix of plastic sheeting and brown paper.
During the course of the project the boat will be taped and re-taped a number of times.

The damaged areas are sanded hard and the remaining gel coat is removed from the area.
This is especially true in crazed areas so we can also check the condition of the laminate.
We use the two pack Nautix epoxy fillers to fair and build up the damaged areas.
A long board is used to sand and fair in order to ensure we get a perfectly fair shape as once the top coat is applied any irregularities will stick out like a sore thumb.

We’ve had excellent and long lasting results using Awlgrip paints over the years and have got to know the system pretty well.
Once the major damaged areas have been dealt with the topsides are coated with the first of three coats of Awlgrip 545 epoxy primer.
This effectively seals the fairing and filled areas as well as providing a good base for top coats.
After the coat is dry we lightly spray a contrasting colour to act as a guide coat and sand back.
The guide coat will quickly show any high spots or valleys which can then be spot filled.
This process is repeated another couple of times until we are 100% happy that the topsides are true and fair.

Everything is now washed, re-taped and a ban on entering the shed so we don’t get any errant airflow from opening doors disturbing unseen dust.
The first of three coats of Awlcraft 2000 topcoat can be applied.
This paint is a two part acrylic urethane high gloss which dries fast and seems to keep its shine for a long time.
Its also buffable so if/when you’re a bit late getting a fender in place you have half a chance to buff out the marks.

Three coats were applied over a 4 hour period. The best time for us to spray is on a Friday so it gets almost three days to semi cure.
Full cure takes a couple of weeks.

Its just a matter of applying the new vinyl stripes and decals and bolting back fittings like boarding ladders and getting her out of shed 3 in one piece.

Compression post repair on a Seamaster 925 – Job Finished –

Whilst doing a little research before starting a new project on a Seamaster 925, I found a quote;
“Holman and Pye design, Seamaster build quality, what more could you ask for?”
The Seamaster 925 that arrived at the yard looked very pretty with classic late 70’s lines and in allround very good condition.
However whoever designed and fitted the compression post was not having a good day or just wasn’t overly concerned about what would happen a few decades into the future.
It was obvious something was wrong from outside, as there was a pronounced bump in the deck, next to the mast foot.
Investigating down below it became obvious what had happened.
For some inexplicable reason the builder had positioned a keel bolt almost directly under the mast compression post.
To enable access to this bolt they built a bridge across the bilge using 6mm steel plate.
Over time the plate corroded and the bridge collapsed due to the rig loads and the deck was pressed down onto the saloon bulkhead, just aft of the post.
Over a little more time the inner skin of the deck gave way crushing the balsa core and created an external bump in the glass outer skin.
Obviously if this continued the deck would have been pierced with the real possibility of losing the rig over the side.

The answer was simple, make a bigger, stronger, more supportive base for the compression post.
Initially I wanted to try and repair without dropping the rig to save the owner a few bob but even with all the rig tension slackened off there was still too much flex in the deck.
Lucky for us our mobile crane can unstep a mast without us having to haul the boat out and so an hour later the rig was sitting on trestles on the pontoon.
The task of getting the old post out, which appeared to have been fitted before the main saloon bulkhead was not quite so straight forward.
There simply was no way to get the post out in one piece and even then a section at the top of the bulkhead would have to be cut away.
The post was made of 2″ galvanized steel tube with a 6mm plate welded to each end.
Interestingly there were no fasteners of any kind attaching the lower plate to anything, relying purely on a couple of layers of glass fibre.
Apart from the lower 4″, the compression post was in very good condition.

The 9″ grinder with a slitting disc took care of cutting off the corroded 4″ of tube and base plate.
Welding galvanised steel is not a good idea at the best of times and access for welding in the boat was also not good, so I decided to make the new base with a spigot that would slide up the inside of the main tube.

Luck was with me as the engineering dept had been fitting new engine beds to a 46′ classic motor yacht and there was a some 80x80x10 stainless angle left over that was just the right length.
We chopped 3″ off an old 1 3/4″ propshaft and that was welded to the 316 ss angle to give us a spigot that fitted inside the post like a glove.
The whole assembly was to be bolted through the Saloon bulkhead so 4 x 10mm holes were drilled in the angle.

The area around the base of the post was taped up with plastic sheeting to try and contain the dust and the hull was ground back to clean glass.
A section of old supporting rib screwed to the lower section of the bulkhead was also removed as there was evidence of water damage, along with the rotten pieces of hard wood used as piers for the bridge.

Using 2″ wide strips of scrap ply and a glue gun, a template for the new supporting rib was stuck together.
I decided to build the new rib out of 4 layers of 25mm thick marine plywood, laminated together using thickened West epoxy.
After a test dry fit a section was removed in the center with a large hole cutter to allow access to the keel-bolt head.

To ensure the loads on the support rib are transferred to the hull effectively its important achieve a close match between the rib landing surface and the hull.
It takes a number of test fits to get a perfect fit against the hull as typically the hull shape differs slightly from one side to the other, a fact that in my experience is normal though it does tend to surprise owners when you point out that their boat is not symmetrical.

Once completed the support rib was then sealed with glass cloth and epoxy.
The top of the support angle was also going to be the bearer for the floor so the support rib height had to allow for the 10mm thickness of the angle and the thickened epoxy that would bond it to the hull.
The last dry fit therefore included laying the support rib on a cardboard gasket to match the required thickness of epoxy in the joint and then the bolt holes were drilled through.
As usual I use a two step bonding process.
The first is to wet out the bonding surfaces with neat resin/hardener to ensure you don’t get any dry patches or voids.
The second is to then add thickened epoxy to one surface before pressing the components together.
Make sure you don’t press too much as all you will achieve is weakening the bond by forcing the epoxy out of the joint.
The 220mm ss stud bolts were inserted and partially tightened and a fillet of epoxy added round the rib/hull joint.
Using a syringe I injected a thickened epoxy mix between the deck and the upper plate.

When cured the whole surface was sanded to remove any sharp edges of epoxy and remove the cure blush before applying two coats of Damboline.
The bolts through the bulkhead were tightened up using plate washers and ss nylock nuts, followed by the upper through deck boats using Arbokol as the bolt sealant.
Finally it was just a case of re stepping the mast, setting up the rig and putting back the interior trim that had been removed to gain access.
As I finished this job a Nauticat 36 was sold locally and the survey picked up a major problem with its compression post.
Guess I know what I’m doing in a few weeks time…….

We’re not great fans of Bow thrusters here on the river.
You simply don’t need them when you’ve got a 2knt flow one way or the other to work with.
So when we hear that unmistakable sound we usually drop tools and watch whoever this latest visitor is, trying to move his vessel sideways into the tide with often hilarious effect.
That said in static water, like a locked marina we accept that they are very handy.
A few years ago I spotted a scalloped bow thruster tube on a Southerly and thought, yeah that’s looks like a good idea.
I could see there would be a reduction in drag compared with the usual eyebrow and probably noise whilst sailing as well, especially when heeled.
So along came an opportunity to try out our own design.
We firstly looked into a retractable thruster as there’s no doubt that these have the least negative effect on performance. The issue is that many yachts simply don’t have the room or suitable layout to be able to install one plus they are not cheap.
So the decision was made to try out our design on a Southerly 38 and after the success of that we followed up with a slightly more technical version on an aluminum Ovni 38.
The performance loss when sailing on these two boats was negligible, maybe .2 knt compared to the usual ¾  to 1 knt we usually saw from the conventional installations with eyebrows.
Yes the installation is a lot more complicated and does require me to cut two dirty gashes down each side of your pride and joy but the reduction in drag and the resulting accidental increase in strength in this important pounding make it well worth it.
The length of the original scallop on the Southerly I saw was in my opinion a little too short.
I’ve always used a rule of thumb that an obstacle will cast a disturbance shadow of at least three times its size at the kinds of speed we sail at. So if I have a 200mm hole I need at least 600mm aft for the flow to settle down again.
One day when I’m rich I’ll do the CFD to back up the theory but at least the practice seems to back it up.

Before we start I should point out that there are lots of ways of doing the same thing, especially when it comes to working on boats.
So the methods I use are the methods I feel most comfortable with, given that it isn’t my boat and that if it goes wrong it’s going to be very expensive.
This pretty much follows for all of our work at the yard.
We’re generally risk averse as failure in part or total is not a good long term business strategy especially as largely our business is generated by word of mouth recommendation and returning happy customers.
So the following is a run of the mill yard job but in isolation it is pretty major surgery with drastic consequences if it fails.
You have been warned.

For a bow thruster to work effectively it needs to be positioned as far forward as possible but needs to be a tube diameter below the waterline so as not to cavitate in use.
Then we come up against the physical limits in terms of available space for the tube and the motor and the necessary access so that the tube can be safely glassed to the hull.
Looking at the hull from the inside can give you a good idea of a suitable location but its often tricky to identify that location from the outside.
So you need to find a datum point that can be viewed from both inside and out that is as close as possible to the proposed location.
Lucky for us this Nicholson 39 has a through hull depth/speed transducer on the center line around 2 feet aft of the proposed thruster location.
So from this point it was relatively easy to project lines marking the bulkhead position (adding a bit for luck) on the outside of the hull.

Once the center point of the tube is found a small hole is drilled through both sides and a 5mm dia rod is inserted through to check alignment both inside and out.
When happy its time to open up this small hole out to 12mm which allows us to use a length of m12 threaded bar as the center line rod that won’t bend during the marking process.

We have a special tool for marking the hole but as with most things in a busy yard its gone walkies so I made a very quick and easy tool which actually worked just as well as the “Special one”.

I still prefer to stitch drill rather than use a 200mm hole cutter.
Yes it takes longer but it is far more controllable.
Leaving the center line bar in place gives you a guide so you drill at the correct angle.
I use a 8mm drill for the stitch holes and usually have to sharpen the drill bit a few times on a bench grinder by the end.

Once the holes have been drilled I use a jigsaw to cut from hole to hole.
Unlocking and loosening the base screw on the jigsaw allows you to keep the blade at the correct angle.
Don’t be tempted to try and cut the entire hole with a jigsaw unless you are 100% confident that you won’t wander off line.
I don’t have such a level of confidence so I stick to stitch drilling.

With the centers removed its an easy if dusty job of removing the rough drill slots using a sanding drum with 40 or 60grit paper.

A few words on the dust.
It’s particularly pernicious, intrusive. smelly and definitely anti social stuff.
You need a FFP3 mask and a disposable hooded overall over your overall.
Inside you need remove everything from the forward cabin and seal the doors.
Even then you will find evidence you missed a bit.
Outside the hull its much harder to control so its damage limitation, we evacuate that shed and the guys move to one of the others, grumbling under their breath until I’ve finished and fired up the vacuum.

Holes in boats are never a good thing.
Huge great holes in a pounding area of the hull are even less good idea.
So I employ a belt and braces approach and ensure I bond the tube externally as well as internally.
To do this I chamfer the outside of the holes so I can get a good 15mm glass thickness around the external joint.
Initially I cut back 50 or 60mm back from the main hole but this will be increased when I get to glassing.

Whilst the nominal dia of the tube is 200mm, because its cut at an angle the largest distance from one edge to the other is 270mm.
So the proposed scallops will need to start at 270mm wide and extend at least 700mm aft.
Looking from the front I can see I’ll need a scallop depth of 45mm.
The next task is to make a mold for the two scallops.

The initial layup of the scallops needn’t be too thick as additional layers will be added later when bonding it to the hull for both inside and out.
The first scallop hole cut into the hull is always a little scary as the hole is BIG and you need to be sure you have it in the right place which on a boat with constant curves is not easy though your eye is pretty good at alignment and often better than a tape measure as many hulls are not as symmetrical as you might think.

Grinding this scallop hole produces prodigious amounts of dust, so sheeting off the area is important and covering every inch of your body in protective gear, vital.
Eventually its a case of grind a bit, test dry fit, grind a bit more, until it all sits nicely together.

Whilst in the early stages we assessed whether there would be sufficient access to glass the tube and the scallop to the inside of the hull, now we have a dry fit you need to look more closely at exactly how you propose to glass it all in.
Obviously the underside of the tube and scallop will be the hardest to get too so I grabbed a brush and roller and ran a test to check I could get to all the joints.
As a result a little more bulkhead had to be cut out of the way and will be replaced later.

When happy with the hole on one side its an easy process to make a cardboard template to mark out the other side.
Then its a case of rinse and repeat.

Moving inside the worst job is grinding back the interior glass to provide a good key.
I aim for a border of clean glass layup at least 6 to 8 inches, followed by scrupulous cleaning of the dust with a high power vac, then a good blast with an airline, finishing off with a thorough wipe down with acetone.
The bonding area of the tube and the scallops get the same treatment before final positioning.

We are using polyester resin and layup as opposed to epoxy.
It’s very much cheaper and faster to layup and the thickness of layup will be immensely strong, the additional weight not being a factor on this boat.
The tube and Scallops are bonded into place using bonding paste, which is the same stuff most decks are bonded to the hull with these days.
The layup is time consuming, especially the tricky glassing under the tube.
I use a couple of mirrors and a long handled brush and roller.
It takes a bit of practice working upside down using a mirror but its obviously imperative that you get a good, consolidated layup.

When glassing the tube it’s worth spending time cutting the glass for each side before hand and laying them on top of each other in order of use.
This is an easy way of ensuring you get an even number of layers on each side as its very easy to lose track of how many you have done.
Due to the shapes and angles involved you have to use short pieces of cloth around a foot long and a maximum of 150 wide.

The first layers are chopped strand as they provide a better grip to the old glass than woven cloth.
Then I move onto 100mm wide biaxial tape and then 450g 150mm wide biaxial tape.

A top tip here is to wet out the glass on a scrap strip of hardboard first and then carefully transfer it to the tube/hull joint which ensures you don’t get any dry areas, at the same time its a lot easier to wet out using the minimum amount of resin which is just as important as too little.
A very common fault of the amateur laminator is using too much resin which will result in a brittle and less strong laminate.
It takes me at least three full days to get all the laminating done, its not something that cannot be rushed.
One of the trickiest jobs is locating the position of the gearbox in the tube.
You only need to be a gnats out and the prop will foul on the tube.
So adding a few strips of masking tape you can mark up the position accurately taking into account that for the prop to be in the center of the tube the motor has to be offset to one side or the other.

Lewmar (bless them) provide a template page in the installation manual to aid fitting. They even call the page “Cutting Templates”.
They then ruin all this work by watermarking the page “Not to scale”! and sure enough they are not to scale but the really frustrating thing is not by very much at all.
Completely bonkers.
So ignoring the manual I use the actual saddle as a template and mark and cutout the require holes.

The owner had decided to locate the thruster battery next to the tube so once the tube and scallops had been glassed, and the gearbox and saddle position settled, the next job is to glass in some shelf supports and then make a template for the shelf.
For this job, strips of gash plywood cut into strips and a glue gun are your friends, a fast and accurate way to template any panel on a boat.
The shelf is made from 19mm marine play and is glass sheathed.
To finish I applied a few coats of gel coat and topped it off with gel coat with added wax in styrene, otherwise know as flowcoat or topcoat gel coat.

Moving back outside the tube and scallops are glassed to the hull and are then made fair.
Scribbling in marker pen is a great way to see highs and lows when sanding and filling.
Whilst the boat was in the shed we had also resprayed the hull and grit blasted the underwater sections and applied four coats of epoxy, then primer then anti-foul.
A point of note here is that epoxy is not as good at bonding to new polyester as it is with old cured grp. The styrene in the layup takes time to leach out during the curing process, (it can take months to fully cure) and this can sometimes effect the bonding ability of the epoxy coating in direct contact. You can speed up the process by cooking the laminate but this is obviously not an option.
So we made sure that the new glass is well keyed and primed and we’ll check on the condition at the end of the season.

The test running will have to wait as the owner wants to carry out the wiring himself which will save him a few pennies, hopefully.
If not, I’ll be running another article shortly on rewiring a partially wired bow thruster.

Small project to fair in the deadwood on a Colvic Watson and installation of a smaller prop