Flat Pontoons

[jdworld]

Also - I am just having nightmares about spending thousands to build this thing, only to find it's a slug. I want to model it as much as I can upfront. ANd maybe literally. Here's where it gets into some physics that I clueless on. If I built little scale versions of my flat pontoons and deck (maybe 1/2" = 1'), and then place weight around on it to simulate the motor, cabin, refer, tanks , and other heavy stuff - will it behave and float in water the same way the full size version would. Will the buoyancy and displacement behave proportionately the same when things are that small?

And then what kind of wood would I use to best simulate a hollow aluminum flat pontoon?

[jdworld]

.....and if the floatation test goes well i might even take it a step further and hang one of these babies on the back and see if she planes!

[PAR]

No offense, but houseboats are slugs. It would be a very rare exception for one to plane, unless is was quite small. You're limiting the design further with pontoon shapes, which requires you to use even lighter weight structures, if you want them to plane.

I guess my point is there is a lot more then meets the eye to this yacht design thing. Many compromises go into each decision and you're just beginning to see some of these difficulties. To have a houseboat, as you've described it and get up an plane, you'll need considerably more "clever engineering" and then it's just an outside shot, unless given enough power. Theoretically, you could hang several large HP outboards on it's butt and away you go, but these ain't cheap to buy, install or operate. Have you priced out 250 HP outboards lately? How about two of them?

A better approach to your problem, would be a skiff or Jon boat hull, instead of the pontoons. You'd be able to carry much more weight and you'd have more area to help generate lift, so you could plane.

What you need is the help of a professional or very experienced amateur designer. Designing these types of structures (strong, light and able to safely have a dynamic relationship with the water) isn't for novices, at least not at this level. A 10' fishing skiff, sure, but not boats this size. There's just way too much to think about, engineer, develop, understand, the safety of loved ones, etc.

[jdworld]

yeah i know i'm pushing the limits of what a houseboat can typically do. But I 'm also part pontoon boat - so i'm comparing to those also. And in researching pontoons out there, there's some Benningtons for example that are about 5000 lbs and they put 150 hp engines on them (and ski behind them). Yes, round pontoons, not flat. But weight wise, not too far off from me. I'll have a big cabin on top, but weight wise still just as light (or heavy depending on your perspective). So I have that to go on. Also came across a company called Holiday Mansion that used to build them. Their's planed and did 30-40 mph. Videos on you tube. Flat wide hull, not pontoons, which I'm sure helped. And yes, they have twin v-8's. Another smaller HB called the Nomad which supposedly does 30mph or so, 5k with a 130 on the back.

So I there's round pontoons about the same weight that do 30+. Flat or shallow vee bottom HB's about the same weight or heavier that do 30+. If I could just get 20mph out of a 150 at 6000lbs with 2 flat pontoons I'd be happy.

I guess the one question is are they able to do those speeds because they get up on plane? I still don't exactly know what defines "plane". When a pontoon boat is going 30+ is it considered to be planing? (even though it doesn't have a "planing hull"?)

[narwhal]

We rented a pontoon houseboat on the Rideau Waterway several years ago; it was an older version of this http://www.threebuoys.com/boatsales.html , about 42' long, and while it was to underpowered for its weight to plane (120hp outdrive), its performance was acceptable. Our criticisms of the vessel were not due to its pontoon design.

I've seen some pontoon deck boats that have have aluminum angle (3x3?)welded longitudinally to the round pontoons to give more bearing to support planing.

[WoodenPontoon]

Originally Posted by narwhal

I've seen some pontoon deck boats that have have aluminum angle (3x3?)welded longitudinally to the round pontoons to give more bearing to support planing.

Those 3x3 angles are called lifting strakes and are designed explictly for that purpose. Most of the newer pontoons with larger engines have these.

[Stefan H]

Topspeed 15,5 knots !!
Size 20 x 6 meter
2 x 160 diesel engines
Glassfiber construction

Weight is unknown...

[Stefan H]

Originally Posted by jdworld

I guess the one question is are they able to do those speeds because they get up on plane? I still don't exactly know what defines "plane". When a pontoon boat is going 30+ is it considered to be planing? (even though it doesn't have a "planing hull"?)

With enough power any hullshape will plane but...

Have you considered making longer pontoons to maximise the displacement speed?

[jdworld]

Originally Posted by Stefan H

Topspeed 15,5 knots !!
Size 20 x 6 meter
2 x 160 diesel engines
Glassfiber construction

Weight is unknown...

haha - that is hilarious! That's taking the word House - Boat to a whole new level. Interesting. Weird, but interesting. A wakeboarders dream boat.

[jdworld]

hmmmm.....i wonder if they ever get any water up over that bow?

[PAR]

It depends on who you'd ask, some here might suggest she's immersed occasionally.

[nightfisher]

I have a friend who owns a 1989 Misty Harbor (they only made the flat pontoon design for a couple years.)

It is an 18 footer wih a 90 yamaha on it. I runs and handles like a boat -- not a pontoon boat. It goes about 30-35mph with two people on it loaded with gear. Every once in a while there is a little spray coming over the front...but this could have been fixed easily by increasing the deck a few inches further forward.

All the best.
Greg
www.ugliboats.com

[ddrdan]

Hey JDworld,
You came to the right place for info. The Pro's on here were an immense help in my design and build process on a build almost similar to yours. PAR is a boat design God!!

I'm a true novice but here's some tips from my mistakes:
Trailered or not? Makes a big difference in the design.

Your power requirements are not just weight related with a house structure on top. It's a dam sail with its own mind!!! lol And as aerodynamic as a tractor trailer. lol

I centered my outboard. I now wish I had put jack plates on both hulls and split the power.

Up the scale on your model. I started small and found it acted like a base ball in water. I found for weight loading tests you might as well just use total load centered to review how the design acts.

Loading the model with specific location weight did not give me true effects on the design. I don't know why, maybe i was doing something wrong, it just didn't work for me. Luckily I built the toons with a temporary deck, launched the rig, and located weight (5 gal buckets - water 8#/gal) on the deck for fixed weight items. I center loaded the super structure (houseboat) weight evenly down the length of each hull as it was going to be a uniform load port to starboard. That method gave me a much better idea of their effects.

I used some of the internal space in the toons for components like batteries, water tanks, etc. No fuel, trust me, you don't want to go there. I integrated the cross members supporting the deck into the hull bulkheads at longer spans and laterally framed between them for deck support. It reduced the deck framing weight by 8%. But I had to increased those bulkhead sizes. It 'almost' turned it into a catamaran style hull.

For the houseboat walls I used 1/4" ply and sandwiched 1.5" rigid insulation between. Fiberglassed the exterior. I fabricated a 2x2 T&G wood insert in the joints of the wall panels I built. I used luan on the interior so you can paint or stain. Another tip, after some research, I found 1/4" sub flooring is almost equal to marine ply and cheaper. And using that lightweight sandwich panel reduced my wall framing requirements.

I also added a 2 step HySuCat foil style chine to the inner sides of the hulls. Although my hulls are flat sides and bottom, not convex like the picture. A pro from another boat forum convinced me it would help. I wasn't wanting it up on plane so I'm not sure if it really did help, but it looks cool?


Good luck!