Modifying Glen-L 32 ft wooden pontoon plans to 38 ft Tri-toon houseboat

[Tom Dugan]

I am wanting to build a houseboat to do the great loop and take down to the keys. I am wanting to find an architect to help with the design changes to the pontoons'. overall length of 38ft with a beam of 11.5 ft. the inclosure will be 30ft x 9ft. will have a front and rear sitting area with a 15inch walk way on each side. I am also open to modifying the pontoons on the Mark Twain 36 or 40

 

[bajansailor]

Welcome to the forum Tom.

Re the limited description you mention above of the boat that you would like to build, do you have an existing design in mind which you like, and which you want to use for reference?
If you do, can you post any links please?
Or have you drawn any sketches of what you have in mind? If you have, can you post copies please?

You mention 'pontoons' - do you literally mean typical aluminium pontoons, or do you want your hulls to be more 'boat shaped' (for want of a better description)?

A beam of 11.5' on a length of 38' is not very wide for a catamaran - in fact it is less than what the beam would be on a typical monohull powerboat of the same length. A typical Length / Beam ratio might be about 3 for a 38' monohull, so it would have a beam of maybe 12.5' - a whole foot wider than your cat, and this is a lot really.

Have you done a search on the internet to see if you can find any suitable second hand boats that will do the Great Loop and take you down to the Cays?
Bear in mind that building your own boat will invariably cost a lot more than buying a second hand boat, not to mention the thousands of hours that will be involved in the construction.
And if you engage a naval architect to help you, that will be a significant additional expense as well.

Edit - I did not read the title which mentions the Glen-L 32' boat - are you referring to the 'Super Huck' 32' pontoons mentioned in the link below?
Super Huck https://www.glen-l.com/super-huck/

Be aware that if you add an extra pontoon to an already narrow catamaran to create a trimaran, then this will increase the resistance enormously (especially so with wave interference effects between the hulls) - not to mention reduce the sea keeping ability.
And you will need reasonable seakeeping ability if you want to take this boat to the Cays (I presume you mean the Florida Cays?)

Edit again - you later mentioned the Mark Twain series (either 36' or 40') - do you still want to convert this into a trimaran (tritoon?) as well?
Mark Twain Series https://www.glen-l.com/mark-twain-series/

 

[philSweet]

I agree that a monohull is better for beams under 13'. You can lower the cg and use the space below the waterline. It also makes more sense for a great looper given some of the air draft constrains both for on the waterway and also for trailering. You might want to just refurb an old Gibson. They were built like tanks in the 60s-70s, and if you are taking it down to the Keys, you're going to need a tank. We had 100 mph winds on average 10 days per year. 135 knots or better 10 days in ten years. The Christmas trades can blow 40 knots for a month. The Everglade National Park concession rented Gibsons.
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[Tom Dugan]

thank you everyone for the response I had originally picked the the super hulk because I was wanting to have a clear platform to build on. I then saw the mark twain. I will definitely check out the monohull. My goal is to make a boat that can handle the loop and keys but isn't set up like some of the trawlers. I would love a big boat but the $ is crazy. I think a RV style boat will give me more room for long term live aboard. I am open to all advice thanks again

 

[gonzo]

Remember that the Great Loop takes you through the Gulf of Mexico for a fair distance in Florida. The keys are also exposed for long distances. The boat you describe is adequate for enclosed, protected waters only. It is possible to make it, but will be completely dependent on having good weather for the whole passage. Also, you say the side decks will be 1.5 feet wide. There should be some kind of railing which will make them narrower. A single wider side deck would be safer. There is no requirement to be symmetrical. If you hire a Naval Architect, it would serve you well to have the whole design made. Many amateurs end up with boats that barely float because they are too heavy, or don't float on the design lines.

 

[Tom Dugan]

If you know a naval architect I would love the help

 

[gonzo]

I know several. However, it is not cheap to get a custom design. Also, the boats you mention, like the Mark Twain, are completely inadequate to go in the open ocean. Even big water like the Chesapeake would be too much in rough weather. You are putting the cart in front of the horse. Start with a statement of requirements (SOR). That will drive the design. From the first draft, you start the design spiral where you see incompatible requirements, missing requirements, etc. If doing the Great Loop is a constraint, a houseboat with 1.5 foot freeboard is out of the question. The Great Lakes are also open water with storms that sink ships. Another very important issue to consider is how many years it will take you to build a 38 foot boat, and also the cost. A crew of four experienced shipwrights can build it in six months if the cabinetry and trim is not too fancy. That is with a well equipped shop and machinery to move heavy parts (at least one forklift).

 

[bajansailor]

If I was going to design and build a boat to do what you are proposing doing I would be inspired by Janthina, a very nice 38' power cat built 48 years ago - here is a copy of a nice write up about her in Boating magazine in 1978.