Construction & refurbish question

Not sure “where” this question should be posted, but it revolves around construction using polyester and glass hulls.

I am taking on a refurbish of a polyester/glass hull finished in gel-coat. It “appears” that some hull “flexing” has added some minor and a few major gel coat cracks. Since all of my builds are with WEST System brand epoxy, I haven’t experienced this and am wondering if any builder using polyester resin and gel coat can suggest or recommend a good method for dealing with the cracks?

The deck is off and I have access to the interior of the hull. Exterior cracks can be sanded back to glass and refinished with epoxy which has a bit of flex and won’t crack. I have considered a very light single layer of maybe 1/2 oz. glass cloth on the inside of the hull, then a sanding back to bare glass and coating with epoxy. Finally will use epoxy thickened to fair the hull which probably will leave a higher flat spot. There are a number of places where the hull needs some “Tender, Loving Care”. I know the epoxy will adhere to the cleaned and “scuffed” polyester, but is the layer of thin glass on interior useful, or just added weight?

Anyone who has done similar repairs, can you provide any suggestions - or identify problems where the repair might not work? As you can see from the photos, the hull in other areas also needs some fairing which will be a part of the restoration. None of the cracks appear to have opened up the glass, and the hull, when filled with water doesn’t leak along the many cracks either.

Thanks in advance for response (and theories as well).


Hi Dick,
imo should not be difficult to use some glass cloth inside after some sanding and acetone cleaning. Externally you need to sand out the residues and apply mastic type used by car body repair.
Finish with carefull sanding and repaint. That’s all.

Some hull flexing?

Looks more like the significant other of the owner has taken a serious dislike to their hobby!!

The cracking in the first picture appears to show some separation of the gel coat from the laminate, which for me indicates one of two problems; either the laminate is too thin or the gelcoat is too thick for the laminate. There is of course a third option, that being that the hull has taken an absolute hammering! As you are no doubt aware one of the main reasons for epoxy being so much ‘stronger’ than polyester is its relative flexibility - polyester resin, and especially polyester gelcoats are essentially brittle by comparison. Actually, I’m minded to think of yet another potential issue on top of those posited, that being that the gelcoat had either cured too much before the glass & resin was applied or wasn’t sufficiently well abraded.

Whatever the cause, I’d certainly agree with Claudio’s solution although I wouldn’t be inclined to use car body fillers - they tend to be polyester based (the exception being some of the ‘high end’ professional products) and are designed for use on fairly stiff panels. Stick with what you know best and use the WEST resin and appropriate modifiers for the external repairs. Whether or not to add additional glass to the inside really depends on the severity (depth) of the cracks and how flexible the existing laminate really is. If flexibility is an issue then it may be worth bonding in some longitudinal stringers and a few frames and/or bulkheads. At the end of the day it’s a judgement call. I’d be inclined to ignore the fact that it’s polyester and just use your experience to carry out those repairs / modifications that you deem necessary.

Good luck with it,



@ Claudio - thanks for your response, Claudio. I have a very fine grinding “burr” (diamond dental drill type) and at about 400,000 rpm, think I will attempt to follow one or two of the more obvious of cracks, grinding out to a depth that will get me to substrate. @ ROW - Thank you as well. The "project’ is an older “TURNER” Marblehead. It has seen better days, but the hull was sent to me for the cost of postage ($ 30 US) so thought I would try to get it back on the water - not competitive - but as a “loaner” to get others hooked. I have a design Claudio did for me of a thin, hard chine, rather flat bottom Marblehead that I want to build just to see how and if my ideas are of any value. My wife will put up with me and my projects, so it isn’t something that she had a hand in. Another thought was that some "stuff’ might have been piled on top while in storage, further adding cracks. As you said, the gel coat thickness might also be a problem as there are couple of areas (other photos) that show it just being “gobbed” on as a possible previous repair. The whole ting looks like it was built OK - but very neglected by a previous, but not original, owner. I think I may start a “blog” to document my efforts to restore her to something that looks nice and sails respectfully. Dick

Photo #1 - looking aft, deck was painted film or mono-kote
Photo #2 - overall view looking down on hull.
Photo #3 - closer look at rudder access, main hatch keel connect and mast tube with reinforcing plate.
Photo #4 - Mast tube and keel base. I “think” tube is aluminum and what looks like rust might be resin. (???)

Hi Dick,
It happen to me to get some culture about repair with real boats once collecting scratches during races.
The West System manuals are very usefull : Please scroll the page to reach the manual of interest.
I suggest to read one of specifically dedicated to lamination repair.
Cheers and Happy Easter

Hi Claudio - same Easter wishes to you and your family.

After some discussion with a friend still working at Gougeon’s shop, our mutual agreements were for me to continue with my idea of grinding out the cracks to allow epoxy resin to flow into them, and on the areas where there is a very poor gel coat applications, I will sand down to the glass substrate. There are also a couple of areas, where I will rough up the gel coat with coarse sand paper, and then add WEST + fairing powder (#470 Microlight) to fill in and add to the locations where initial rounding of hull has some flat spots with no fairing at all. Without the fairing, one can see obvious places where there are flat panels (I think) - especially along the center keel line of the hull.

I have tried to find out if the original design had a flat bottom of the hull - but have not had any definite answers - so I may leave the very bottom of the hull rather flat. There doesn’t look like any easy way to make the bottom of the semi-circular, unless I tear it open and rebuild using balsa strips. If I am going that far, I would rather build the multi-chine “M” design you provided.

Best wishes.


Arrrrgh … started the demolition today to get rid of extra “junk”. Sure wish I knew the history of this thing, and who built it and who worked on it. :confused:

To start, I began removing the cover plate on the mast tube. Interesting - There are several circles in a wood stringer that allow the mast tube to be lifted and moved fore and aft. Great idea except ----- someone broke the thin aluminum mast tube and tried to fix if by wrapping fiberglass cloth and resin around it. Result: failure and the cloth prevents the lifting of the mast tube for a different location. (See photo below) ---- this is looking down at structure that held mast tube, and the yellow base block could be lifted and the tube raised and relocated. As noted - it was a unique idea, but the damaged sidewall of the mast tube was now a limiting factor.

On to the deck - while trying to remove some of the Mylar or mono-coat several of the wooden cross-hull deck supports lifted out with the fabric - thus indicating a loss of adhesion to the gunwales. Next was the removal of the “contraption” holding batteries, servos and Rx. This was a nightmare design. It slide behind a screw at the front, and was screwed to a block of wood that was fastened (???) to the bottom of the hull. The slightest pressure on the wood block caused it to lose adhesion to the hull substrate.

Moving to the hatch area, the deck was cut loose, but I need to find a small screw driver and using an Xacto blade to clean the slots in the screws I can remove it - although a chunk of 1/2 cross beam came loose - again, a questionable glue job. Finally got the rear deck off and found that the rudder tube was the only thing holding the base resin fillet to the hull — or had held it at one time. Now tube is loose and can be lifted about 1/8 inch with resin attached. Of greater concern, the cross-beam holding the top of the rudder tube was cracked and split between some weight-reduction holes drilled though it. Looking at the bottom of the keel where rudder post would exit - the hull looks deformed and pushed in. Can’t tell if the rudder pushed up - or if the area was sanded flat to let the rudder turn from side to side without rubbing on the hull.

Anyway, got rid of stuff and dropping weight at the same time. I must say, whomever built the keel trunk knew what they were doing. A nice, professional job, and finished clear. Can’t tell if hull is carbon or just glass painted black.

A QUESTION: The mast was located 2-1/2 inches (about 6.5 cm) in front of the leading edge of the keel. Any way to tell if this was for a swing rig - or for a traditional rig location?

Hi Dick,
I got impression you are enjoying this type of work !!!
If it is a class M, most probably should refer to a Swing Rig, but confirmation should come from the sail plan.
As rule of thumb, the CE should fall within the first quarter of the Fin chord up to the leading edge.

OK - will layout the sail (“A” size - one that I have) on the floor and see where it falls.

You are correct - this is going to be a challenge. Want it to look nice, and sail reasonably well - if not fast. :rolleyes:

Hi Dick here below the typical sail shapes of Class M Rig Type A for Classic and Swing rig.
As you can see the distance of the CE from mast is 25mm about for the classic and about 65mm for the swing.
Distance increase at deck level if mast is raked

Hi All - who may have an interest. The Marblehead demolition, and reconstruction proceeds. After a considerable amount of searching, plus a bunch of knowledgeable skippers over on the RCGroups forum, the following are some of my findings:

  1. The boat is approximately from the mid to late 1980’s and was designed and built by an East Coast sailor, last name of “TURNER”. It was modified at some point to handle a swing rig, and the name of possible rig designer is Jon Elmaleh.
  2. The hull is a fabric composite, but too flexible to be carbon, even though it is black in color. It looks to have a white gel-coat (or paint) and hull sides are very flexible - thus the small cracks - but I wouldn’t be surprised if it was involved in some on-water collisions, or maybe had the hull damage from poor, unsupported storage.
  3. It definitely was assembled using using polyester resin, and many attachment support items have broken loose around the perimeter of the resin “puddle”.
  4. I have proceeded to remove all interior parts with the exception of the mast base/keel trunk, some cross-hull timbers, and have yet to attack the rudder support and rudder post. I have cut and am replacing some of the cross beams at deck level with new basswood - but sealed with epoxy prior to gluing in between gunwales.
  5. Because the hull was so flexible, I decided to add a very thin veneer to the exterior of the hull. Then stain, and fill any small spaces between the veneer strips with microballoons. Finally will add a coat or two of epoxy with a very thin (1/2 oz/sq. yd.) glass cloth. This should add a bit of abrasion resistance as well and handle any slight variations between veneer strips. (These past several weeks have tried my patience as there have been tremendous humidity changes. One day the strips lie flat, the next day there are some strip edges that have lifted. Will attack these when doing the epoxy coating when all veneer is done.)
  6. The hull design has a flat bottom section and then has curved hull sides. This is a challenge to veneer, and at certain angles, it almost looks like the center of the hull is raised slightly. It is an optical illusion because of the curve to flat, plus the veneer strips are angled to allow compound bending.
  7. Because of the changes in humidity, not much stripping has been done. The 2 inch wide strips are laid on at an angle that lets the strip bend to the hull curve - and also to fit to the keel rocker line which is significant and can be seen in the full side view. The stern section of the bottom of the hull (rocker) really rises.

Planned work to be done:
A. I plan to add pieces of sheet balsa inside the hull where flexing still takes place. Will be a coat of epoxy, a piece of 1/64th. thick, 3 inch wide balsa sheet, coated on top with epoxy and covered with wax paper (or plastic shopping bag) so I can lay weights on the balsa to take on the shape of the hull. The plastic will prevent my weights from being glued to the interior of the hull. The weight added will be minimal. I had coated the interior of the hull with straight, non-thickened epoxy and while it help remove flex, there is still too much for my liking.

B. Complete the addition of cross hull deck beams and restore/rebuild the rudder support , log, and base block.

C. The hull came without a keel, bulb or rudder, so today my wood arrived for the fabrication of the rudder, the keel blade, and the mast. I ordered 2 pieces of #1, clear, Western Red Cedar (no knots). The plan is to strip-cut the boards, and then using thin slices, laminate the strips to appropriate thickness, length and shape. Strips will have an orientation to provide fore/aft and side to side stiffness. Since this boat will be a 50/800 (as opposed to a Marblehead) the tip of the mast “may” be bent to form the mast crane, and I may decide to include a permanent mast bend. If the process works, a new mainsail will be needed and will be of a rectangular shape, tapering at the head, and will probably have a “fat head” top. (Non-Marblehead compliant) With plenty of wood, I may also decide to laminate strips into a swing-rig format since the inner swing-rig supports have been left in the hull. Time will tell on that.

The keel blade will also be a series of vertical lamination and be oriented to each other to provide the strongest, non-bending blade possible. While it may not be the most accurate NACA profile, it should be “close enough” for a cruising and play boat with limited racing concerns. Similar process for the rudder.

Once the veneer is protected, I will tape the rudder tube and the keel slot, and add weight to get the boat to float on where I think the waterline should be. From there it will be a matter to estimate the weight of rig and sails, radio gear and batteries and then cast a bulb. I am seeking sheet lead at the moment to try Claudio D’s bulb making concept using thin slices of lead, cut to shape, glued up and then finish formed.

That pretty much brings us up to date. I might take time out, as I purchased a Joysway “Force 60” catamaran and want to get it on the water and try sailing it before winter arrives.

Some photos of veneer application follow.

String stretched on center line between bow and stern. Light spray paint. Remove string when paint is dry to see center line.

Start of the veneer laminating process. Slot is bottom of keel trunk.

Side view of 3 strips of veneer added to existing exterior of hull.

Starboard side view of hull - six strips of mahogany added.
Color difference is the darker was left from a previous 1 Meter veneering
Stain will even out all colors

A look at the starboard side of hull. Veneer strips have been trimmed at top of gunwales.
Bow section will be removed, as cork was used for bumper. Will be replaced with new, cast silicone
bumper that will be softer.

Well, you’ve certainly got plenty of work with that one! I particularly like the veneer finish - it’ll look really good when done. Any idea what the additional weight of that finish is likely to be?

Good luck with the rest of it,


Looks great dick…

@ Row - no idea on weight. I may weigh a package of veneer when done and try subtracting the weight remaining package - but kind of inconsequential since this boat isn’t competitive with the current designs. Besides, it is being built as a " 50/800 " and while similar to a “legal” M it probably won’t be, as I am thinking of a strip-laminated mast with built in bend, and a faired in mast head crane and boom goose-neck connection (although a legal rig might be project #2) since it won’t have to support a fat-head main or worry about jib termination height, bands or cross sections of mast/booms. In fact, the rig #1 might be built to sail as a uni-rig which (on one of my RG65’s) has shown to sail much higher to windward.

Not taking a shot at the Marblehead class in general, only observing a lot of technology changes since the class began. Just feel that as a development class, it hasn’t really moved forward as much as I thought it would. Regardless, there are a few near me that aren’t raced, so when done, I may buy breakfasts for the owners, just to get them to come out so I can sail against them and see where the old girl has her problems - if any.

Almost done with one side of veneer, and then will start on the other side. May do a partial finish on the completed side … stain, micro-balloon any spots between strips, and then a single coat of epoxy. If I decide to glass, I will do that all at one time. Underwater body will probably be flat black with white, yellow or red waterline stripe. At least my thinking right now.


@ Marc - thanks for your complement. Hope it turns out the way I want it to.

Ive seen other projects of yours I have no doubt its going to be a functioning peice of art…

I still have so much cherry veneer that I have use up at some point…