Alternative to an inflatable keel?

dim. · 16 July 2008, 21:25

Is there any for SIB's?
I tried to pump keel in my boat up to an 8pci. It still flex. I am thinking to stick metal pipe (removable) filled with a cement mix between keel and bottom or keel and all. floor ... Not sure if it worth to try however.

prairie tuber · 17 July 2008, 06:28

You should not be pumping your keel up beyond 3.5 - 4 psi. It doesn't matter if the keel flexes. The purpose of an inflatable keel is not to provide rigidity to the boat. A SIB's rigidity comes from the main sponsons and the floorboards. The purpose of an inflatable keel is to help with tracking and and to soften the ride in choppy conditions.

dim. · 17 July 2008, 15:12

Well ... according to specs I have to pump it to a 5.8psi. But it handles 7psi no problem. I once forgot to top it to a specs and it was very unpleasant ride. Soft keel cannot produce enough tension for a bottom material and water and air buildup in the end of the boat (underneath) causing weird boat behavior while on the plane. Hard keel chops through waves better than a soft one according my observation.

Sadly but my aluminum floor does not provide rigidity I would like to see :| That is why I would like to place solid bar underneath it.

jyasaki · 17 July 2008, 15:46

Some of the older Bombards have a wooden keel. I suppose you could replace the inflatable tube with a custom fitted piece of lumber, but I'd worry about the strength of the floor fabric.

jky

dim. · 17 July 2008, 16:31

Quote:

Originally Posted by jyasaki

Some of the older Bombards have a wooden keel.

Do you remember model name? I'll try to search for assembling instructions. I suppose it would be difficult to assemble floorboards after fitting wooden keel in place ...

jyasaki · 17 July 2008, 21:52

Quote:

Originally Posted by dim.

Do you remember model name? I'll try to search for assembling instructions. I suppose it would be difficult to assemble floorboards after fitting wooden keel in place ...

I want to say a "C5"? About a 16' big black monstrosity. Probably from the mid-80's. Maybe.

I am going from memory here, as the owner of the particular boat replaced the wooden floor with some huge slabs of diamond-plate aluminum (not cut the same as the originals.) But, the keel itself, I think, was in two pieces. The rear-most and front most floor panels attached to the two keel pieces (bolted in, I believe.) Insert the front into the bow, the rear either up against or under the transom (sorry; don't remember now), then lever the keel joint down into place, stretching the boat. I think a couple of metal plates bolted over the joint to make it rigid. Then the rest of the floor was inserted, and the last pieces levered in in the same manner as the keel. Side-rail stiffeners were inserted to lock the floor pieces together, and the boat was inflated.

jky

Apparently, I lied. The keel was in 3 sections (no idea how it went together.) Some kind of no-tooling joinery. You can see the brochure for Bombard 2008 here:
http://pdf.nauticexpo.com/pdf/bombar...0348-6231.html
You want to look at page 15.

prairie tuber · 18 July 2008, 05:28

Quote:

Originally Posted by dim.

Well ... according to specs I have to pump it to a 5.8psi. But it handles 7psi no problem. I once forgot to top it to a specs and it was very unpleasant ride. Soft keel cannot produce enough tension for a bottom material and water and air buildup in the end of the boat (underneath) causing weird boat behavior while on the plane. Hard keel chops through waves better than a soft one according my observation.

Sadly but my aluminum floor does not provide rigidity I would like to see :| That is why I would like to place solid bar underneath it.

I was thinking pressure for hypalon, but yea, if it's PVC the maximum pressure would be higher. Is the aluminum floor flexing primarily at the joints between the sections or throught the whole boards?

Channel Ribs · 18 July 2008, 10:37

Quote:

Originally Posted by dim.

Is there any for SIB's?
I tried to pump keel in my boat up to an 8pci. It still flex. I am thinking to stick metal pipe (removable) filled with a cement mix between keel and bottom or keel and all. floor ... Not sure if it worth to try however.

You may like to look at ways to strengthen the floor rather than the keel, perhaps side bars that overlap every board?

dim. · 18 July 2008, 17:16

No. Not joins. I have side bars. It is like whole floor bends for a moment and flattens back again.

dim. · 18 July 2008, 17:20

jky, thanks for the link. At least it is possible

captnjack · 18 July 2008, 20:00

The Bombard C3, C4 and C5 all have wooden keels. Not designed to work on flexing as much as provide a deeper V (they have hinges). Although you can bolt them together and that helps a little. If you don't have one of these boats, building a wooden keel is no small task. The fabric may need reinforcement and it may not help much absent more V anyway.

If your floor is otherwise installed correctly, you need a different boat or milder sea conditions.

geoffs · 19 July 2008, 18:23

How about some custom shaped hard polystyrene panels to go between the floor and the material of the hull. They would be light and still flexible, but prevent the hull from forming pressure pockets. Might give it a try on mine if I start getting the same effect. Maybe a business opportunity for someone

Poly · 21 July 2008, 16:18

have you thought about making the whole keel, and deck from GRP. then you could make GRP "running surface" on the hull too and just have the tubes around the outside...

oh wait someonese already done that...

dim. · 21 July 2008, 19:52

Quote:

Originally Posted by Polwart

oh wait someonese already done that...

Who?

Ideally I would prefer keel-shaped air deck underneath my aluminum floor. Not sure if some one can make it.

dim. · 21 July 2008, 20:01

Quote:

Originally Posted by geoffs

How about some custom shaped hard polystyrene panels to go between the floor and the material of the hull.

Thought of that. Still have no idea how to hold them on place as close as possible to hull material. Inflate soccer balls on each side?

Poly · 21 July 2008, 20:53

Quote:

Originally Posted by dim.

Who?

Ideally I would prefer keel-shaped air deck underneath my aluminum floor. Not sure if some one can make it.

it was an attempt at being amusing. you seem to be looking for a stiff/solid hull/keel and stiffer deck - the answer is of course to get rid of the inflatable boat and buy a RIB.

dim. · 21 July 2008, 21:03

Quote:

Originally Posted by Polwart

it was an attempt at being amusing.

Shame on you

Quote:

you seem to be looking for a stiff/solid hull/keel and stiffer deck - the answer is of course to get rid of the inflatable boat and buy a RIB.

Well answer is right but circumstances are wrong. Unfortunately. I have storage issue as for now. So that is why I am open to an ideas as long as they would not cost too much.

Poly · 21 July 2008, 22:04

Quote:

Originally Posted by dim.

Shame on you

Well answer is right but circumstances are wrong. Unfortunately. I have storage issue as for now. So that is why I am open to an ideas as long as they would not cost too much.

I guess there was another point though. Which was - it probably will cost money, take effort and diminish many of the advantages of a SIB, e.g. portability in terms of size and weight

m chappelow · 22 July 2008, 18:30

i have known people to fill keels or tubes with expanding foam but it stops the inflate /deflate aspect of the boat .

jyasaki · 24 July 2008, 16:19

Someone mentioned to me once that there was a solid fiberglass insert available that fit under the keel and floorboards to hold a more rigid V. Never heard anything else about it, though, so it may have been smoke. It was supposed to be for an Achilles SIB.

jky