Approach to molding and laying up a coastal rowing boat

Hello,

I am an absolute beginner boat builder and would like to build a coastal rowing boat, similar to the Wintech Coastal (https://www.wintechracing.com/coastal-boat/). I understand that this project is ambitious. But I am hoping that you all who are more experienced can point me in the right direction.

While I have the shape in CAD and know how to make the molds on a CNC, I have no idea how exactly to approach designing the molds for the top part of the boat. By my current understanding, this boat would have to be done in two molds - one for the top and the bottom.

In the case of a coastal rowing boat I am confused exactly how to achieve any part that is not the hull.


Should I create a hull and a deck mold, do the initial layers of the layup, and then glue them together and add another layer of fiberglass outside to join them? Is that even a good idea for a boat of this type? I have checked out some scull manufacturers pages but did not find any info on how they do their molds. Do you guys know of any good resources?

Thanks in advance

 

How many boats are you planning on building? The process is that you first build a boat (the plug) from which you make the molds of. Then you make more hulls/decks from the molds. That means that for the first boat, you have to make three.

 

I don't know exactly the process you have in mind but I have never needed to build three hulls to use only one. The mold is made and with it all the hulls, all of them useful, that the builder needs are obtained. @Luke Rhoas, what information do you have at this time? I would like to help you and, as you can see, the most expensive is not always the best. Put yourself in the hands of someone with real experience.

 

I plan to build only one boat. I intend for this boat to be hollow for weight savings. From what I know so far, making a hollow boat in the shape of what is designed (shown in the image in the original post) is not possible with one mold. I do understand how to make a kayak using a female mold, but this coastal row boat I plan on building has features that enclose it, such as that triangle feature near the bow of the boat. This makes me think that two separate hull and deck molds are needed. Maybe a better example of what I am trying to grasp is the Literace 1x (LiteRace 1X - Liteboat https://www.liteboat.com/rowing-boat/literace-1x-solo-coastal-rowing-boat/), which clearly distinguishes the hull and the "deck" part, as can be seen in this picture:

 

If you want to use two molds you must first decide how to join the two halfs of the boat (hull and deck). On the photo you posted of the Liteboat you can clearly see the overhanging deck, it is glued on a corresponding flange molded into the hull. There are other ways, like for example with an inward flange, etc. Basically you create an overlap between the two halfs and glue them together with thickened resin or some other adhesive. What you propose, no flange and glassing over the outside of the joint is also possible, usually the area is slightly recessed to ease fairing. This type of joint is rarely used in series production because it requires fairing and painting afterwards, so gelcoated boats don't use it.

For a one off this size you can also use male molding. The plug is carved (by hand or CNC) from polystyrene foam (EPS or XPS or both) the hull is laminated completely over it using epoxy or a polystyrene safe polyester (or you cover the foam with something styrene resistant and use regular poly/vinylester), painted and faired, then the foam is removed by dissolving it with acetone or gasoline inserted via a hole (one hole is mandatory anyway, you need some form of pressure equalization, and often an inspection or cargo hatch is also fitted). Laminating ribs and bulkheads is possible but it must be done before the skin, you carve them and their flanges into the plug (for bulkheads you cut the plug completely).

 

Seems like the OEM already shows the top and bottom molded pieces via colors blue and red:


I like the idea of CNC'ing this out of EPS and glassing with epoxy, similar to a surfboard or strand-up paddle bard. I would leave the foam intact to prevent the hull from crushing, installing the proper breather vents for EPS. Using a lightweight EPS, I imagine the weight penalty of 4-5 lb (2-2.5kg, you can take the enclosed volume and do the math) would be a good trade in a much simpler build and increased durability. It will be difficult as a first time, one-off builder to match the structure, weight, fit and finish of a factory-built specimen.

 

I’ve built many one off fiberglass parts using a lost foam technique.
Shape the foam, glass over it, then remove part or all of the foam.
Hull half, deck half with joining tabs turned inwards, scoop out the unnecessary foam and glue them together.
Don’t forget to add a drain plug.

 

The heart of the matter is the decision whether to build over foam as a one off or to prepare for the possibility of further boats and create the tooling to make subsequent boats much faster to get to completion.One significant problem with building over CNC cut foam is locating a large enough machine.Many businesses will have a 3 axis CNC router that will cut 8'X4' sheets but finding a large 5 axis machine is not so easy and the use of it will probably come at a higher cost.You might try machining slabs that a 3 axis machine can deal with and then assembling them,prior to glassing.Having completed both hull and deck surfaces you will be faced with the challenge of holding it in it's correct shape while the glass skin is being applied and no doubt something could be worked out.

For more conventional moulding you are more or less obliged to create a plug and then take a mould from it.You can,and I have,made female moulds directly and you have the choice of CNC machining or old fashioned boatbuilding to do the job.The hull to deck joint is something that has to be thought about in detail and the image in post #4 is the simplest solution as it is a small horizontal flange from the sheer line of the boat with an overlapping deck bonded on top of it.This means a single piece hull mould is possible as well as a single piece deck moulding.You could arrive at something like a Laser hull/deck joint if you had a good idea of the laminate thickness and this would act as a great handhold ashore as well as a spray deflector-but it is a bit more demanding.It would need some form of stiffening beneath any areas where weight is applied and the easy solution is to make a section of the deck moulding and determine the actual shape that they need to be.If you have confidence in the accuracy of the hull and the laminate thickness,you can get pretty close just by offsetting the skin thickness of the CAD model.

I have to admit that if i wanted a one off it would be wooden and cold moulded as the process would be much more enjoyable to me,but if I thought that others were likely I would take a mould from it for the purpose.

 

One off the quick and dirty way would be to build a plug out of foam, fair it, glass it, finish it and use it. I built a number of such craft years ago, hot wired sections of eps, glued together; it was fairly quick and easy and I learned a lot along the way. Today I'd use xps foam and a client used same on a 48' x 15" beam trimaran hull I designed for his 3 man pedal powered racer a couple of years ago.