Recommissioning of an old hull mould

Hello everyone.
I'm new to the forum, but I'm not new to the world of polyester or naval design. However, some of you seem much more knowledgeable than I am and offer excellent advice.

This topic might also be of interest to some of you.

The story:

I stumbled across an old boat mold and bought it on a whim. I think I got a good deal.

For now, I've just given it a good pressure washer and turned it over to inspect the bottom of the hull, take my measurements, and plan future designs.

The boat is 8.70 meters long and 2.70 meters wide amidships. It's relatively low, 1.35 meters at the bow, but its lines are correct.

I therefore want to put this mold back into service and use it, not industrially, but several times. So there's work to be done.

My problems:

The foam reinforcements are quite worn.

First of all, the exterior has been very poorly maintained. After a pressure wash, the fiberglass looks like it's fraying, as if the polyester has evaporated from the surface.

Inside, the gelcoat isn't too bad, but there are still some cobweb-like cracks.

The foam reinforcements are quite worn and there are numerous breaks, but more importantly, I find the mold relatively thin.

My plan of action:

So I'm going to take this mold back to my shed and start by re-coating everything with polyester, for free, repairing all the broken structures and then thickening everything with 3mm Coremat.

Then I'm going to turn the thing over, repair the cracks in the gelcoat, sand it, wax it, apply PVA, etc.

My questions:

Does my plan of action seem logical?
Do you think my new thickened polyester coating will adhere easily if the surface isn't too dirty?
If not, I could try sanding everything with 60 grit, but I'm afraid I'll remove a lot of material before I reach a truly "healthy" area.
Do you also think the cracks will reappear quickly?

 

Welcome to the Forum Makloko.

Can you tell us a bit more about the mould please, and ideally post a few photos?
Is it for a motor boat or a sailing boat?
Re how you want to build a few hulls with it, have you assessed that there is a market for selling these hulls, or will you keep them for yourself?

You mention that the 'lines are correct'.
Are you sure about this, because you later note that the mould is relatively thin, and there are numerous breaks in the foam reinforcements on the outside.
Hence there could be potential for distortion?

There are fibreglass experts on here who are much more qualified than I am to offer an opinion on this, but in a nutshell I would answer this with a 'no' - if you want to build up the thickness of the mould with additional layers on the outside you will have to first grind the whole surface well and then clean it.
If you suitably reinforce the exterior of the mould, and repair the cracks in the gelcoat on the inside, then there is a good possibility that the cracks in the gelcoat will not reappear.

If you can post some photos of the mould (inside and outside), that would be useful.

 

Hello Mr. BajanSailor,
Thank you for your reply.
This is for an outboard use, pretty simple design. No mould for the deck.
Indeed, there is a small market.

Actually, I'm not 100% sure that there are no deformities, but it seems that this mold has not been used much and that the wear and fractures are more related to the way it was stored.
I don't really know how to check its integrity other than by eye. If anyone has any ideas... It won't be easy to wedge it properly so that it's completely straight.

Here are some pictures of the monster.
When I found it :
Cleaning it :
Returning it :
The inside :

 

Your plan seems plausible and ought to work.It will require a lot of effort,but you seem to understand that already.Some pictures would be helpful if you nave posting privileges.The cobweb like damage to the gelcoat are almost certainly the result of somebody hitting the mould with a rubber hammer to bring about the release of a hull by shock and eventually some damage is done.Grinding open the cracks and adding new gelcoat is tedious but totally possible,but there is a risk of the repair being visible on surfaces that won't be covered by antifouling paint.They can be polished away with a bit of work and the repairs to the mould may not stay in place for more than a few hulls-which may be sufficient.

Before doing anything as radical as sanding the interior surface with 60 grit,try cleaning it thoroughly.Water and detergent will be a good start and if there is a possibility of frost,you need to dry it well so that frost does not cause more damage.If inside in a workshop that doesn't experience freezing temperature,it should be OK.Look carefully for scribed waterlines and if necessary tape over them while polishing the mould,they will be extremely useful later and will need to be re-applied.similarly,there may be reference lines on the outside that you ought to take care to keep as setting up a mould to be level is much easier with some known datums.There are various cleaning products that can be used to polish the surface oxidation off the gelcoat and I don't know what options exist in France,so can't make product suggestions.Once that point has been reached,you can evaluate the condition and determine the best way forward.

By this stage the mould may not seem to be such a bargain but may still have enough life to allow a hull to be made.Don't overlook the designer's right to a royalty if hulls are produced and he will probably be able to offer advice in return.

 

I see that pictures appeared while I was typing.The mould was intended for use with a stand at each end that held the tube which protrudes and would have been rotated to allow access from the workshop floor to the low side when the mould was on it's side.Having those stands would be a big bonus.If you need to work inside the mould when it is upright,you may need to add local support beneath the keel as it doesn't seem to have longitudinal bracing along the keel line and may feel bouncy as you walk around.If you have any amount of experience in dealing with mouldings,you won't need to be told that walking on the inner surface with ordinary shoes is a bad thing.Shoes that are only used in the mould and which have clean soles should be kept near the mould and ideally on a piece of cardboard where ordinary shoes can be left while inside the mould and replaced on one's feet when leaving the working zone.

From the appearance of the inside,I would estimate that you have a good chance of getting a satisfactory hull-with a bit of work.I have seen worse moulds brought back to limited life.

 

Hello Wet Feet,
Thank you for your reply!

Unfortunately, the designer has passed away. I haven't found anyone qualified to have worked on this mold.
I'll look for any references I can.
Normally, frost isn't a problem where we are, as the climate isn't that dry.

I was referring to sanding the entire exterior to replenish it with pure resin, then 3 mm Coremat.

In France, we have almost the same products as in the United States, I believe. With a good soap, polishing paste, and a good polish, that should be enough to bring the gelcoat back to life, right?

 

Indeed, the mold was certainly used suspended at these two ends. Given the thinness of the laminate, I'm not sure it's always a good idea to work like this. I'm afraid the boat will warp, even if the keel is wedged as you suggest. What do you think?

 

If you apply coremat and a some glass over it,the mould will become quite a bit more rigid,It will also become heavier.With such a large bond area,it shouldn't be too big a problem if the total bond area isn't absolutely perfectly bonded,but a clean and dry surface to apply the coremat to is very important.If you can retrieve the stands that were used to support the mould,life becomes easier as you can rotate the mould to avoid having to work overhead.

I am a little surprised that you are having difficulty finding people with the ability to repair the gelcoat.it is a common task in areas that have numbers of boats in use and the need to use tooling gelcoat for compatibility doesn't make a big difference.I would expect the mould to have been made with tooling gelcoat,but it is a colour that I haven't seen here in England.We normally buy black,green,orange or red,but there is no reason why other colours could not be used and it is possible to make a mould with ordinary laminating gelcoat,the difference being that tooling gelcoat is orth-pthalic and less flexible.

 

Thank you very much! So, in principle, there's no need to sand the entire exterior if it's clean. I'll clean it more thoroughly and saturate it with pure resin. I think the frayed fabric should respond well to this process. Then I'll apply the coremat

My English is not very good, but what I meant to say was that I haven't found anyone who has worked on this mold before and who could advise me about the waterlines, etc.

Thanks for the stands supports, I had already searched without success, but I'll continue my search. Otherwise, I'll build them myself.

I've never seen tooling gelcoat in this color either, but I guess it's not a big deal. I'll repair it with whatever gelcoat I can find after grinding the spider webs.

I'll keep you posted on my progress, but this isn't my main project.

 

I may have been confused about the surface you were proposing to sand.I would avoid sanding the interior gelcoat,but the exterior glass may have types of contamination and you will have better success if you can apply resin to a well prepared surface that has a possibility of bonding to new material.

Coremat without glass on top of it won't make much difference to stiffness,so some glass would be a good idea.

I think you should be searching for drawings of the boat,or a friendly owner who would permit you to take measurements of his hull and the interior arrangements.Positioning heavy items,such as engines and fuel or water tanks will have a big effect on trim and need to be in their designed locations.This will also dictate many aspects of the interior layout.By measuring the sheer height of a boat in the water you will have some kind of reference to apply to your project.What type of deck do you propose?

 

Okay, for now, I'm thinking more about renovating this mold than about the final model.

In fact, I'm not going to grind the inner surface, except for the areas that are cracked in places. I'm just going to redo the polishing, 220, 400, 600, 1000, 2000, polish, wax, etc.

On the other hand, the outside is another matter. The mold is very thin, so I'd like to make it thicker to make a few casts, but I have to work economically because I'm not sure if the mold is really straight. And I don't really know how to check that, as there aren't many reference points in the mold. That's why I was thinking of adding coremat. I could also add some foam reinforcements, but I don't want to redo the whole laminating process with several layers of mat, etc. Maybe I'm wrong about this?

Fortunately, I've already worked on an old model made from this mold. I converted this inboard boat into a twin-engine outboard by adding a plywood epoxy bracket of my conception, so I did a buoyancy study and am familiar with the weight distribution, etc. What's more, this boat is still in my workshop and I can take all the necessary measurements.

 

For glassing the outside it shoul be cleaned with more than water. I usually use a sandblaster to clean surfaces with many corners and hollows.

 

Stop before you do anything.

Just adding coremat to the outside is useless, you need to add glass then coremat, then more glass, and the surface needs to be thoroughly cleaned and sanded with 36 grit prior to laminating on it. And it may need none of that work done if all you do is use it a few times.

On the inside it's sort of the same thing, don't do any extensive repairs to the mold surface for just a few hulls. It is very costly and time consuming to resurface a mold, in a situation like this its easier to fix the cosmetic defects on the hull surface after its been built. Buff it with coarse compound, then a polishing compound, thats it. Plus much of the surface will have bottom paint on it.

And I'd be surprised if you build more than one (if that) These old molds are given away frequently because there just isn't a market for the design or it would still be in use.

And you mentioned you were doing the outside for free, how can you do it at no cost?

 

Re the first photo that you posted, in the background there is a boat with the number AC 719 818 on the side.
I was just wondering if maybe it came from the mould shown in the photos, but the bow shape is wrong, and it has chines, which are not visible in the mould.
It does however look like a much more useful kind of boat, when compared to what your mould will produce.
Once you build a hull with this mould, what sort of deck / superstructure will you put on it?
Do you have any drawing / sketches to illustrate what you would like to do with it?

 

Thank you verymuch for your advices !

Commercially speaking, and considering the design of the mold, I am certain that I can use it several times.
However, I don't know if the mold will hold up once I have renovated it. Perhaps it would be better to create a one-off, give it a nice surface, and make a final mold.
I didn't explain myself well if you think I can work on it for free. On the contrary, my resources are limited for this project, and I don't want to work in vain.

Thanks for the advice about stripping and adding fabric to both sides of the coremat.