Buoyancy collar (foam vs inflatable)

I am considering converting a 19' deep-v center console to a rigid inflatable or adding a buoyancy collar for additional offshore capabilities. I would like to hear your thoughts and suggestions regarding the feasability of this project (as opposed to the sanity of it). Specifically, I would like to hear from Rasorinc, as he had a post on a similar thread mentioning that he was already fabricating a product like this out of styrofoam billet. Regards

 

Gemini Tubes

http://www.geminiindustries.co.uk/rib%20tubes.htm

This is a link to a company that produces inflatable tubes for RIBS that are about as affordable as I've seen. It is also a company I'm familiar with from previously shopping for ribs. I am including photos of my project boat as well. Other modifications I am making are sealing the deck and compartments to keep water out of the bilge and replacing the small self bailing factory scuppers with larger 2" or 2.5" drains.

I live on the Texas Gulf Coast where 1' seas are common throughout the summer and 3' are the norm. The continental shelf is 40 nmfrom shore and you have to run 75nm just to find 100' of water. I typically fish 10 - 30nm out in water less than 40'. I am not looking to extend my range, rather to be able to fish more days and handle rough water better when the summer storms kick up. Not particularly concerned with comfort or dry ride, but safety.

My first thought was to just add styrofoam billet inside the gunwales or below decks, but was concerned about the placement of the extra weight. I didn't want to alter the center of gravity and center of buoyancy that would result in a boat that would remain positively buoyant if swamped, only to turtle ond float keel up. I also like the idea of a larger footprint created by inflatable tubes.

 

forgot the pics

 

http://www.boatdesign.net/forums/boat-design/converting-rib-25460.html#post285036

This is the link to a better thread where I will be updating the status of my project. I have made some good progress in getting the total cost of materials down. I was going to wait for winter to start construction, but it looks like I may be done before the summer is over.

 

Watching your progress.. with intrest

 

Buoyancy

jefflee2k,

Are your objectives to keep your existing boat, increase your safety

margine by having amply positive floatation and to increase your rough

water capabilities when the sea kicks up?

The last one I question as your tubes will likely never touch the sea.

In a traditional RIB this is the case.

Have you considered calculating if filling your void spaces with foam would

create positive floatation?

To me, this would be the way to go.

Your windage will increase, your fuel consumption will increase, your resale

value will drop (in most cases, unless your buyer thinks just like you which

is entirely possible but most people don't like major modifications).

I would think long and hard before taking this one on.

Just my thoughts. Good luck.

Tom

 

The objectives you've noted are correct. I want to increase flotation, but also the effective size of the boat, or its footprint in the water. The tubes will be large enough and low enough to support the boat at rest but nearly clear the water while on plane. You raise some good points which I have already considered:

Resale value: a non issue. This was a project boat from the beginning. I reconditioned a salvaged hull, and have very little invested. I enjoy boat and tinkering and have alot of free time.

Adding underdeck flotation: I can gain an equal amount of buoyancy with slightly less weight gain by keeping the foam inside the hull, but by moving the flotation outboard I improve the balance of center of gravity to center of flotation. I am worried that if I simply foam the hull and I should swamp the boat, that while it may still float, it will flounder and float keel up.

Gas consumption: I do recognize that i will conceed gas consumtion at displacement speeds, but should maintain similar consumtion at planing speeds. However, I have enough horsepower to handle the extra weight while planing, and use a auxillery motor to troll and run at displacement speeds. The small motor runs wot anyway, and the nonplaning speed of this boat is 6-8 knotts. Theoretically this shouldn't change much. Also my objective is to increase the rough water capabilities of this boat. If I had to buy a bigger boat, my gas cunsumption would definately increase.

Gas consumption and rough water capabilities are my biggest concerns/objectives. I am looking for more feedback like this from people who are wiser and more experienced than I am. Thank you Tom. If you still think I am making a mistake, please let me know. All advice is greatly appreciated. Also, I have started posting all my updates on a better thread below. Click on:

http://www.boatdesign.net/forums/boat-design/converting-rib-25460.html#post285036