Houseboat pontoon question

[Jim Hawkins]

My lifelong dream has been to build a houseboat, now that am am ready to build I need to finalize my plan. The boat will be small for a house boat, 10' X 30' because I am limited to 10' wide in my canal in the Florida Keys where I will moor it. I want the boat to be stable and seaworthy for near shore waters so I considered adding a third, 24" X 24" (approx.) center fiberglass pontoon.

It occurred to me, although I'm not an engineer, that if I lower the center pontoon by 2, 3, or 4 inches more than the side toons it would increase stability as far as taking a roller on the beam. Does this wash?

 

[ahicks]

Not an engineer either, so take this for what it's worth.

First, I would avoid weather where there's much concern about taking a roller on the beam.

Second, though I like the 3rd 'toon plan, I'm thinking lowering it might ADD to the top heavy feeling a boat like this might have when something like that happens (side to side rocking horse effect? Like a round bottom boat?). If anything, you might be further ahead lowering the outside 'toons if stability is the concern.

Last, If I were going to the trouble of building something like that, I would likely go to 40' or more. On a cost per sg. ft. basis, I'll bet that move would really pay off later on with the extra room it provides, even if it were just extra deck space. My thinking anyway..... -Al

 

[HotTommy]

I estimate that lowering a 24" x 24' log an extra 4" would displace at most about 16 cubic feet of water. That would increase the lift from the center log by about 1000 pounds. I doubt you would notice the difference on a houseboat. .... If you are thinking that lowering the center log would make the boat act more like an outrigger canoe, my intuition tells me the distance between the center log and the outer logs is too small to have much effect. I agree with ahicks' sentiment and I would avoid large swells and waves at all costs with a houseboat.

 

[Jim Hawkins]

Thanks guys,

There's no way I can go 40' but it would be nice to have the extra room.

I wasn't thinking it would be like outriggers, it is really just more of a feeling I have when imagining the feel of a boat rolling. Yes, I believe it would be much more like a rounded hull like a sailboat so instead of having a square box lifted and slammed back down by a wave it would have some "roll" that it seems would smooth out the action of the wave passing

 

[garbageguy]

Intriguing thought. HT started, and I think more numbers should be looked at. Do others do that? Most of these innovations have been worked out, and the most practical are,at least somewhat, put into "production" - but hey, you never know. I agree that if a craft like that is to be designed to take rollers a-beam, then that's a design consideration

 

[Jim Hawkins]

The extreme case would be where a rouge wave actually flips the houseboat (square box) on it's side and with that in mind it just feels uncomfortable to imagine the bottom all in one flat line. No doubt this has been looked at by builders I just wonder what they came up with. I think all single hulled cruising houseboats have a lower center keel.

 

[ahicks]

The reason for the lower center section of conventional hulls, in my mind anyway, is about providing lift. To get the hull up on top as speed increases, lifting as much of the hull as possible out of the water for reduced drag. Same story with later tri-toons. Benefit with larger/deeper center with tri-toon is also to allow the boat to bank in hard turns, ridding them of an uncomfortable lean to the outside otherwise. Guys with the larger engines on a conventional twin tube 'toons can speak for that, pretty sure....

 

[Jim Hawkins]

ahicks, thanks. I was not aware that some tri-toons use a deeper center toon but I can imagine it would make for better maneuvering just going by the same gut instinct. I did a quick search and found what you mentioned. I also read that a lower center toon will make the boat rock a little more but in most situations at anchor I don't think that will be an issue, still much less than a sailboat.