Small speed boat mold construction

[Chopperr007]

Hey, I’m going too make a little speed boat at around 8’ long -- debating on the type but am definitely going to use a mold so I can reuse it. I'm new to this so I was wondering what the best material I could use, or what I should laminate it with[the material]? I want to do both top and bottom and then use a extruded aluminum to connect the two halves. I'd appreciate any and all help y’all are willing to provide. Thanks tons.

 

[bajansailor]

Do you have a design in mind for this little 'speedboat' or are you going to design it yourself?
If you do not yet have a design in mind, do you have any photos or drawings of similar boats that you would like to use as a basis for reference?
How much power will this speedboat have?
Re reusing the mould, how many boats are you hoping to build with it?

I want to do both top and bottom and then use a extruded aluminium to connect the two half sides

I am a bit baffled here - do you want to build the mould in two halves that are joined together, and can be disassembled for releasing the hull when it is ready?
What do you mean by 'top and bottom'?

Is this mould construction related to your other thread in the link below?

Thread 'Want to diy a speed boat and was hoping someone who knew thier stuff could tell me hell yea or no'

Aug 6, 2026

I’m thinking ide be better off choosing power source and then the drive train.Iwas going to go with a 1.8L naturally asperated with a surface drive speed prop and have the ability to move it up or down as needed I was thinking that ide like to put that in a 9 or10’vhull and locate the engine in front of me ,not too far forward.I don’t have a lot of money so I’ll have to get creative with making it a 2 speed so the prop doesn’t cavitation off the rip,and my diy trim will be easier to do.so I’m wondering or hoping that someone will look at this post and give me a heads up on whether I’m on...

• Chopperr007
• boat diy small speed
• Replies: 14
• Forum: Boat Design

 

[Chopperr007]

Yes they would have like a extruded aluminum that went all the way around ,like some boats have now ,it would have a slot the top half would fit in and a slot for the bottom half ,and the face of it would accept like a trim around it 2”or so to hide the mechanics behind it.so the mold would be a inverted image of what the finish product would be,top and bottom .i suppose I could permanently seal the two but the advantages of being able to take it apart are a lot .and it would almost be unsinkable.and being able to take them apart would make the boat so somebody could configure it in anyway they’d like ,just drill the rivets. Because that edge would have a thin sheet of aluminum glassed in it so it couldn’t pull apart. And the reason ide like to go the mold route is because I have bad shoulders and very little money so ide like to sell them seeing how I’m 65 and bouncing around in it would hurt ,but all the same I like building stuff and been wanting to build a boat for a while and that’s not heavy work ,working the surfaces to a shine would be the hardest part.The boats I’m concentrating on are ones you put a outboard in between 8’to10’,so you could put a pretty big motor in them .and that’s one of the advantages of being able to separate them is because you could put a little weight in it .Not sure if that’s feasible.but the gas can could be located in the front with a lid like a car or one that the new owner could install .as long as you take care of the mold you could get a lot of boats out of it .yea if you have some pics to share ide like to check them out.and the mold is no longer needed for the boat when I pop the boat out and the half’s would be like from the deck up and the deck down goes that help? Oh yea I’m gonna do the thing where I put it in a bag and suck the air out so no bubbles.

 

[bajansailor]

If I understand you correctly, do you want to build a mould in the same fashion as a jetski (eg a Yamaha Waverunner), where you have a hull moulding and a deck moulding, and then the two are joined together with an extruded aluminium rubbing strake section over the two flanges where the deck and the hull are joined?
If so, then it would definitely be better to have two separate moulds rather than a one piece mould.

And the reason ide like to go the mold route is because I have bad shoulders and very little money so ide like to sell them seeing how I’m 65 and bouncing around in it would hurt ,but all the same I like building stuff

Be aware that mould building is very good at eating up cash like there is no tomorrow - have you calculated how many complete boats you would have to pop from the mould(s), and sell, just to recoup the initial investment in the mould materials (not to mention all the hours of labour that you would have to put in to the project to get a decent finish on the mould?
I am also 65 (almost), and my shoulder joints are knackered now, and they complain furiously as soon as I do anything with them, even just gentle sanding.

If you have very little money to start with, then your best bet would probably be to buy (or even find for free) a boat that is in need of some slight restoration.
Building a new mould to produce an 8' speedboat will cost a LOT more than any little 8' - 10' speedboat in reasonable condition.

Oh yea I’m gonna do the thing where I put it in a bag and suck the air out so no bubbles.

I think you mean that you want to vaccuum bag the components to suck the excess resin out?
I don't think this is necessary for a little 8' boat, unless you are looking at making a high-tech very light (and very expensive) boat with a carbon hull and deck.

There are many others on this Forum who have much more experience than I do re GRP boatbuilding - like @ondarvr and @fallguy and @Rumars - if they offer opinions on here, take note.

 

[ondarvr]

With so little information provided there is no way to give an accurate answer.

Best products...an engineered carbon fiber and epoxy prepreg laminate made on metal tooling designed by someone that specializes in this exact size of powered boat. But that's not what I think you are asking.

Making a mold for an 8' speed boat and then making a couple of them, by someone that has never worked with fiberglass before, sounds like a multi year project and $15,000 to $25,000 plus in costs. Is that in your budget?

If you want a small speed boat look on market place and buy one, they pop up fairly often. You could drive 1,000 miles each way to get it and be far better off than trying to build something from scratch. And there are probably some molds out there looking for a new home if you really wanted to build them.

Starting from scratch means you need to understand all the design concepts of an 8' speed boat first, then do testing. Now you need to build the exact shape for each plug, then build the molds, which will cost significantly more than the parts you will make off of them. Now you need to go back and build both the hull and deck. So you've built each part three times, six parts in total, to get one finished part, and that's if it turns out good.

And when you've gotten this far you'll have found out you could significantly improve the design and start modifying stuff.

I'm only saying this because I've been down this road with dozens of builders of all sorts of things and this is how it turns out.

So unless you have a solid reason to design and build this boat, you should probably go buy one.

 

[TANSL]

Option 1: The OP is clueless and doesn't know he could buy a pre-built boat.

Option 2: The OP, who isn't clueless, wants to build his own boat and is asking for advice on how to do it.

In both cases, those of us who have never built a boat, or only one, shouldn't muddy the waters.

 

[ondarvr]

Option 1: The OP is clueless and doesn't know he could buy a pre-built boat.

Option 2: The OP, who isn't clueless, wants to build his own boat and is asking for advice on how to do it.

In both cases, those of us who have never built a boat, or only one, shouldn't muddy the waters.

From what he has posted it sounds like he has a real desire to build a small boat, but with little to no knowledge of how to do it or what's involved. At 65, not in great shape, and with little money, achieving that goal sounds unlikely.

And he wants to sell them, which will require quite a bit of time and energy just to get a new design approved for retail sales. This size of craft isn't that popular, there have been many companies try to build them and soon find out that while everyone will tell you it's a great design and they'd love to have one, they won't actually spend a dime on it. A marine design engineer that is a good friend of mine started a company to do this exact thing, it didn't work out that well. Even after a couple decades of experience in the industry, and a great design, after a few years of building them the money and desire ran out.

I did 30 years in the fabrication and production side of the industry prior to jumping to this side of it, so I know how hard it is to start an operation like this. That difficulty is compounded if you don't have any experience with the materials.

 

[tpenfield]

I built an 8' boat . . . it is basically a pram dinghy . . . fiberglass over foam core. I didn't know enough at the time, so it could have come out better.
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8 feet is not much in terms of a size . . . Mercury built a small 'speed boat' often called a Mouse boat, as I believe they were featured at Disney World . . .
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It sounds like this is what you may be after.

If you want to make a mold for re-use, then you will probably want to follow a 'plug-mold-part' process. I used this process when I made an extended swim platform for one of my boats. (there is a thread on here with all the details - just search for 'custom extended swim platform' )

The 'Plug' will be an exact size/shape of the boat, usually made out of foam and finished with epoxy or similar material to get a nice smooth/shiny surface. From the Plug, you can then make the mold . . . usually starting with tooling gelcoat and then building up layers of fiberglass. A re-usable mold will need some structural reinforcement on the outside. I would recommend viewing boat factory tour videos on Youtube to get a visual of the process and what the molds generally look like.

You will probably have 2 molds . . . 'hull' and 'cap'. They usually join at the rubrail. This may be what you are talking about with the aluminum, but I'm not sure that will be the right approach. Usually the hull/cap joint is a shoe-box style for power boats. My sailboat has an external flange joint, but you don't see those too much with powerboats.

As for materials . . . Vinyl Ester resin . . . biaxial cloth . . . (1708 and 1808 for multi directional strength) . . . foam cores for weight savings & strength.

Your boat should have positive flotation so that it is USCG compliant. So think about that. Boats sold in the USA require a Hull ID Number (HIN) . In small quantities, you can/should get the HIN from the local state agency that is in charge of watercraft. Each state has their own 'MIC code' which is the HIN pre-fix. I got my HIN for the boat I built from the nice folks at the Massachusetts Environmental Law Police.

Got any sketches/drawings of what you are planning to build ? . . . it should help with further replies and guidance.

Oh, and go get some money . . . I would think $10,000 would be a good starting point, but it may lead to more.

 

[TANSL]

From what he has posted it sounds like he has a real desire to build a small boat, but with little to no knowledge of how to do it or what's involved. At 65, not in great shape, and with little money, achieving that goal sounds unlikely.

And he wants to sell them, which will require quite a bit of time and energy just to get a new design approved for retail sales. This size of craft isn't that popular, there have been many companies try to build them and soon find out that while everyone will tell you it's a great design and they'd love to have one, they won't actually spend a dime on it. A marine design engineer that is a good friend of mine started a company to do this exact thing, it didn't work out that well. Even after a couple decades of experience in the industry, and a great design, after a few years of building them the money and desire ran out.

I did 30 years in the fabrication and production side of the industry prior to jumping to this side of it, so I know how hard it is to start an operation like this. That difficulty is compounded if you don't have any experience with the materials.

The OP probably has 10 or 15 years, or more, of an active and productive life ahead of him. Why would he give up on such a wonderful project just because, according to you, he's too old?
A "marine design engineer," a profession I know absolutely nothing about (I don't know what qualifications they might have), isn't necessarily a good entrepreneur. The fact that your friend failed doesn't mean that everyone who starts this business is destined to fail. In general, an engineer, of any kind, isn't a good entrepreneur; their technical training doesn't give them any special advantage for success in business.
Have you actually started a small boat building business? Could you tell us more about this fascinating experience of yours? Thank you.
I have been speaking for over 30 years, from my business, and working with and for shipbuilders, large, medium and small factories, and I do not feel qualified to advise anyone who wants to undertake this type of business, how they should carry it out, nor to predict certain failure.
So, based on what we know so far about the OP and their intentions, I encourage him to go ahead.
Cheers.

 

[Chopperr007]

I want to build a small boat around 8ft to 10ft. I want to sell it too fund the build of more boats, but I also want to build the type of boat that would be desirable and sell quickly. I plan to build a fast one.in hopes of drawing attention too it.One of my questions is, should I build a hydroplane or a v-bottom. I am open for any ideas or suggestions. Thank you for the input.

 

[bajansailor]

Have you done even some very basic market research to find out what type of boat would be desirable and would sell quickly to folk in Georgia?
Or are you more ambitious, and you want to sell nationwide (or even further)?
Starting off locally is probably better, and using word of mouth advertising
Have you asked Google for a list of all of the other boat builders in Georgia, and then you looked them up to see what sort of small boats they are building for the local market?

 

[ondarvr]

The OP probably has 10 or 15 years, or more, of an active and productive life ahead of him. Why would he give up on such a wonderful project just because, according to you, he's too old?
A "marine design engineer," a profession I know absolutely nothing about (I don't know what qualifications they might have), isn't necessarily a good entrepreneur. The fact that your friend failed doesn't mean that everyone who starts this business is destined to fail. In general, an engineer, of any kind, isn't a good entrepreneur; their technical training doesn't give them any special advantage for success in business.
Have you actually started a small boat building business? Could you tell us more about this fascinating experience of yours? Thank you.
I have been speaking for over 30 years, from my business, and working with and for shipbuilders, large, medium and small factories, and I do not feel qualified to advise anyone who wants to undertake this type of business, how they should carry it out, nor to predict certain failure.
So, based on what we know so far about the OP and their intentions, I encourage him to go ahead.
Cheers.

That's fine if he moves forward with this project.

He described himself as not able to do much work due to his physical limitations, and has little money.

I've worked with countless people with similar dreams because I'm the one they contact for advice and products to build the tooling. Plus I'm old enough to know how much energy someone at this stage of life has, and I'm far healthier than he described himself to be.

Even if he has the motivation, where is the money going to come from? He said he wants to make additional income to support himself....because he doesn't have much. He will need to fund this project from his wallet for a few years before he will be able to sell anything, if that ever happens. He also needs to learn the world of composites, government regulations, marketing, financing, production, insurance, and I almost forgot real estate because he'll need a place to build them.

And from working with boat builders for the last thirty years, none have been successful at building a small speed boat like this, not even one. People just don't want to spend the money on one when personal water craft outperform them in every way and there are so many choices.

Sometimes there needs to be a voice that says, "maybe you should think this through a little better before jumping in". Its frequently not what someone wants to hear, but if he had an actual plan and there was a market just waiting for something like this, it might be a better opportunity.

And my friend, smart guy, knew what he was doing, the boats got great reviews, and he had connections due to his time and position in the industry. What it came down to was people wanted to buy something else because this size boat is too limited in what it can do.

 

[bajansailor]

Chopper has also started this thread in the Boat Design Forum - it would have been easier if he had simply asked his question here.

https://www.boatdesign.net/threads/at-odds.71047/

I agree with Ondarvr - there is simply not a market for what Chopper has in mind.
If somebody wants a general purpose 8' tender for their yacht, there are so many designs already out there that are very suitable for the task.
Many are sold as plans only, for people to build at home.

If somebody wants a little speedboat, the average RHIB (of which there are many) will 'do the job' very well.
Here is a typical example - an 8' inflatable with a fibreglass floor that can take up to an 11 hp outboard engine. And with 11 horses on the transom she will certainly shift.

Caribe L8 - Caribe Tenders

The smallest one of the Light models, with all the special features of this series, a built-in runner for fuel line and a bow spot for a portable fuel tank.

caribetenders.com

The advertised price is 2,731 euros, which is approx US$ 3,150.
Chopper, do you think that you could manufacture and sell an all fibreglass 8' boat for this price and make a small profit?

And as Ondarvr has noted, the most popular boats by far seem to be the personal watercraft like the Yamaha Waverunner.

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[tpenfield]

Perhaps @Admin can combine the 2 threads, since they are the same topic. Hopefully, @Chopperr007 will reply and speak for himself now that a few of us have offered their advice and experience.

I tend to agree with @ondarvr on the business side . . . I think more 'boat companies' go out of business every year than go in business. . . but perhaps the OP is thinking small scale . . . a few boats, more as a hobby than a business.

 

[Boat Design Net Moderator]

Threads merged now to keep the discussion together.