small backyard built houseboat

Thank you in advance for putting up with a rookie boat builder (and the english measurements). I joined the forum because it seemed like a good idea to run my backyard boat past some experts before I begin building it. This project seems like it's way beneath most of your expertise, but it's a stretch for me. I have done some research on these forums, wikipedia, read some of the coast guard materials, found the ABYC H-35 safe loading document, etc. so I have a minimal understanding of some of the principles involved. Anyway, I have had the idea to build this boat for decades and I'm going to begin building later this winter. The purpose of the vessel is mostly for fresh water, but maybe I can attempt a few hour stint in the gulf of mexico someday if the conditions are decent? I'm trying to keep it simple, so I decided I'd use pontoons with an outboard motor setup.

I attached a spreadsheet with some details and basic calculations. I also attached a picture of one of my models to give you an idea what I'm thinking it will look like. I tried to make my models to scale for size and weight. My current plan is for the boat to be 24' long x 11' wide. When testing my models, I realized that keeping the boat to the maximum trailer width of 8'-6" was going to make the boat kind of top heavy/tippy in the water. So I have been thinking I would go with an 11' beam to keep it a little more stable. I found a few options for crank up style pontoon/houseboat trailers that will work for towing this. I'll need highway permits and wide load stickers and will have to take my time getting anywhere.

I initially thought I would use aluminum to construct the frame that ties the pontoons together and supports the deck. After some research, I realized that the material will be about 2x the price of steel, and the welders that can handle 1/4” aluminum are quite expensive. And I have no experience working with aluminum. If I could snap my fingers and have it done, I'd go with aluminum and save the extra 450 pounds and rust. But due to the expense and difficulty of construction, I am leaning towards using steel in order to save money and construction trouble. If I prepare the steel properly and paint it well, I think it will hold up fine. Steel works well for automobiles and trailers, and the truth of it is that this vessel will spend 99% of it's time on land sitting in my field next to my other trailers. I'm going to have to be sealing the cedar decking every year anyway, so maybe it won't be that much trouble to touch up the frame paint at the same time.

In the model, I have a cantilevered section on the bow that would primarily be for seated passengers. I will need help from one of my engineering buddies to dial in the cantilevered beams, but it seems doable as long as I keep the cantilever relatively short and make sure the bow won't dip too low when people are up there.

Regarding flotation, I already bought my pontoons and they are sitting in my field ready to go. It might be the cart before the horse, but they were the only pontoons I could find at 36" that weren't enormously long, and I knew I needed all the buoyancy I could get. The figures for the buoyancy on the pontoons should be accurate as I have a certified testing report given to me by the manufacturer. The pontoons are foam filled, so there are no voids inside of them. I tried to research actual weights in my spreadsheet, except for the cabin; I had to do some guessing with that. My plan is to weigh everything as I'm building and eliminate the toys in the cabin as needed. If I have to, I can buy a matching 3rd pontoon, but I'm trying to keep that space open for fuel, storage, etc. if I can. It also makes the overall weight more difficult to pull behind a normal tow vehicle. I understand the “pontoon effect” principle that for 2 pontoons, I can never put more weight on this craft than one pontoon can support. And I'll make sure I weigh the thing at a truck stop before I think about setting her in the water.

In the excel workbook, there are 2 worksheets. The 1st is the details for the houseboat weight and flotation. The 2nd is an attempt to figure out how she will move around in the waves compared to other boats I've been on. I'm not sure if I even got the formulas right, let alone figure out what they mean. I just don't want her to be too tippy or give anyone whiplash if we hit some windy conditions. I've been on houseboat's in lake Powell and they seem fine when they hit a wake, so maybe this will be ok too. Thanks for taking a look at my project.

Thanks,
Greg

 

I am not a smart boat person - that is the disclaimer.

Good job on the 36" pontoons, and not recycling 24" pontoons from a little deck boat.
You stand to actually have a decent boat out of this, I think.
Hows your height?
Max trailer height is 13 ft I believe, and I couldn't figure out how to make a houseboat with 36" pontoons that would still fit on a trailer, have full height cabin, and be within limit.

I believe you should be good to have steel frame with aluminum pontoons, but you want some kind of plastic bushing used to connect the steel to aluminum, not just bolted together.

When I was thinking of a similar idea, I was contemplating having the pontoons fold out 90*, so that you get 36" of deck on each side of the 8'6" wide cabin, but folds in for highway legal width.

 

Thanks. The pontoons are actually plastic with stainless threaded inserts to bolt to the frame. The final height should end up at about 12' on the trailer, but definitely something I'll have to keep an eye on when building the cabin. The canopy will be removable or collapsable, so just the height of the cabin is the issue. Thanks for the heads up on that, as I wasn't really considering the road height limit. It would create quite a mess going under a bridge over the standard height limit.

 

Captain,

You may want to look into getting an annual oversize permit, instead of doing them one at a time. I don't know the rules for your states, but in many if you get the permit then you are allowed to tow it anywhere you want so long as you abide by the time/road restrictions. At least in Louisiana I can get an annual permit that allows me to tow up to 16' high and 13' wide that only restricts me from major interstates and surface roads during weekday rush hour, and a few other high traffic places on other days.

I know Colorado has such a program, but I don't know the details.

They should also have a map of the bridge height restrictions, road restrictions, ect that you may want to be careful of.

 

I'd be scared to pull anything remotely getting to 16 ft high, thats gonna catch wind like a son of a.....
I thought of making one with a "pop up" camper.
but just would be so much work.

 

7' of headroom (generous), plus 3' of pontoon, is 10' on a trailer say 2' off the ground, leaves good clearance.

Windage is always an issue with with this type of craft, but a big enough engine can overcome a lot. Your cantilever doesn't look very severe, so you'll be okay, if the supports are scaled sufficiently.

Calculate you pontoon sinkage with everything imaginable aboard, including guests, Fidel the wonder dog and all the coolers full of beer the deck can tolerate. No more then 50% immersion on the pontoons, preferably less with everything, including the kitchen sink aboard.

A 24x8.5' boat isn't as unstable as you'd think and will save a fair bit of trouble dragging it about. 10' width permitting isn't such a bad thing and fairly cheap, but if you go 11', you'll need oversize permitting (much more costly in most places), with flag cars front and back, etc.

 

I'm concerned about towing your 8,000 ++ trailer as well as your width and height. Oversize means less usage to me because of the hassels. Every state will issue you a permit for a 10' trailer with no restrictions-- they just want a few bucks. A lighter boat will mean a lighter tow vehicle and at 8,000 + pounds your talking a 1 ton truck or more.

I will give you some food for thought. Look at this plan, making it 10' x 30' and design a cabin for it and the interior you want. Much lighter, very sea worthy, and faster than a houseboat, very stable, inexpensive to https://www.boatdesigns.com/products.asp?dept=528 build, and easy to build--21' are a flat bottom.
Just an idea for you that might be easier to use and to complete. ps don't know how the link got in the middle instead of the end.

 

But anything over even 8.5 ft wide still needs a permit I think, just when you go over 10, you need pilot vehicles and stuff.

Don't forget when you say "7 ft of headroom", the roof will eat up an easy 4", the floor and beams will eat up an easy 4"
And 24" isn't much room for the trailer wheels and spring travel.

 

Parkland, could you please pull that giant photo? Thanks.

 

Speaking of houseboats

on Apollo ducks

 

Good to see a new designer actually do the math on a project -

Based on my own past mental exercises, the concept of using pontoons is only an illusion of simplicity. By the time you join them together, sit stuff on top of them, try to store stuff in them, you make yourself a lot of work.

I have a personal resolution that a project this size and weight would be a 'barge' ( hollow hull ) arrangement, that could give you immensely better room for weight, and you could attach axle/wheels to, and save the problem of trailer building as well.

The actual hull scantlings would be an easy exercise for a reasonably priced NA, and the build of one hull would be easier and possibly cheaper than two pontoons, with all the associated problems, to my mind.

A single hull might be worth investigating before going the pontoon path.

 

Watson you've taken the words from my mouth Over in the east state of OZ There is a boat club that launches boat and trailer together, then motors with trailer on to deeper water, anchors the trailer and goes of fishing, reverse the process coming home So a barge or at least tunnel hull pseudo cat might be the best way of building a say 25 by 8 floating caravan and surely its possible to have triple wheels with sealed bearings and just leave them on. why have a trailer .Interesting whats more stable 25 by 8 barge or pontoon cat ? Narrow cats have a bad rap in nz for getting rolled so I think a barge shape with a vee bottom in essence a scow

 

Agreed, as those that know me would understand. I'm not married to the barge hull, but at least a single hull, where you can have soles below the LWL, decks just above, propulsion hidden away below decks, tanks and plumbing, etc, all below decks and a much more efficient hull form, which is easier to live with come time to fill 'er up. My Egress design is 28' and only needs a 20 HP outboard.

 

Thanks for all the feedback. A single hull is intriguing and I didn't really consider it, mostly because I have no confidence I could make a hull water tight and stable. After seeing that example with the 500hp behind it, I kind of regret not looking for something like that I could use as a base. That vessel looks like it can handle just about anything, and probably can hold 2-3 times the weight of my pontoons. I haven't started anything yet, so I'll continue to ponder the idea.

Thanks for the advice about the highway towing and permits. I did some quick research and it appears I can get an annual permit here in Colorado for less than $200. If I take it out of state, there appear to be many websites where I can plug in my route and they send me the various state permits. So the expense doesn't seem to be too big of an issue, just the logistics of towing the vessel very slowly wherever I'm going. I also found out the magic number for width in Colorado is 13'. Anything over that requires a lot more money and hassle with pilot vehicles, etc. I think the minimum width I can make this boat, and still use the crank up style trailer, is 10'. I might consider just making the boat 10' even if it doesn't save me the permits. At least I'll have 6" of space on either side to fit in a standard width highway lane. I don't think I'm going to make many friends driving down the highway in either case. Fortunately the closest lake is only 2 miles from my house.

 

Maybe there needs to be a space. (it has a difference of R vs r in 'river' )

This works...
http://georgebuehler.com/River Walker.html