Inflatable boat restoration...

[Hard Rock]

I have a 1990 Zodiac inflatable boat used by the US Navy. I purchased it as part of a lot in an auction. It had two holes in it whichare now patched. I want to restore and modify this boat but I have some questions and desperately need some help. The boat is a 15 man inflatable that is 21 feet long and weighs 210 pounds.

First off, the boat has an inflatable floor. I'd like to convert this over to a rigid floor but I don't know how to proceed. Should I remove the inflatable floor (this will leave the keel materal intact)? How do I go about making the rigid floor?

Secondly, I want to reinforce the bottom of the boat. Someone told me that I can purchase a spray on rubberized coating that will add thickness and durability to the underside. Does anyone know where I can get this stuff and some good quality black paint that will work on the boat?

Last thing, the boat seems to be in good shape, I've taken it out several times with satisfactory results. I am using a Mercury Marine 30 hp engine on it. Any advice?

Thanks for any answers,

Mike

[Windy]

Mike,

Youcan buy heavy duty chaff material from whitewater boat builders, try sotar.com or wing.com. also do a web search for whitewater boats and you can probably find one close to you for material and some free advise. Another option for the bottom is to build a rigid shell from fiberglass. If you can keep the floor inflated you can use a release wax and start laying up the fiberglass right ontop of the floor, of course the boat has to be upside down!!! add a hypalon pocket for the rigid hull nose to slip into and bring the back right up the rear of the transom. The motor will lock the hull in place and the rigid hull will still be removable. I would not get rid of the inflatable floor because it keeps everything where it is suppose to be. Again you can make interior floor panels from fiberglass that follow the contour of the inflated floor. Remember to use lots of release wax, which can be washed off with mek or any strong solvent when the job is done. as far as painting the tubes you can buy hypalon paint in any colour from hurricane in BC.
Canada. The good paint will cost you about $500 and will last over 10 years. There are cheaper paints out there but one usually gets what one pays for!!!

If you do a good job on the ridgid bottom you can trade in that 30hp. for a 90 or bigger. Next project will be the center console. Good Luck

[gonzo]

Soft inflatables and RIBs are built different. If you just attach a rigid bottom to the soft sides something will fail.

[Windy]

The rigid bottom creates a smoother faster running surface which means improved performance. If the boat is repowered with a much larger engine you can extend the rigid hull under the back half of the tubes. This eliminates tube flutter but starts to complicate what was a really simple hull shell. Soft bottom inflatables are basiclly a full bottom displacement with the tubes always in the water. This is what makes them so smooth to ride in and extremely stable. You want to keep the tubes skimming the water for that great stability. If your rigid hull is no more than 2 or 3 inches thick you will retain these qualities. all that's required is to add a nice strong hypalon V-pouch for the fiberglass nose to fit into and as I said bring the rigid aft section up the outside of the transom. Lock it together with the motor securing bolts and add a few extra bolts if it makes you feel more secure. If things start to come apart rebuild them - only stronger!!!

[gonzo]

A 2"-3" thick hull would be adequate for a 90'boat. It would be in the 3/16" vicinity. Of course you need to calculate it for the load and HP you are planning. Also, what is your sugestion for attaching the bottom to the sides?

[Windy]

I don't suggest you build a solid glass shell 3" thick, but you could use some core material to add shape to the bottom. When completed the shell should be no more than 3" thick. The tubes do not need to be attached because they are seamed to the inflatable floor and supported by the transom. Happy New Year - Have a great 2004

[gonzo]

A rigid floor backing up the soft one would create structural problems. For example, the seams would be stressed more because of the increased bottom loads. Also, if the rigid panel is not attached it will chafe the tubes and cut them.

[Windy]

The whole thing is really easy to do and doesn't cost too much. The biggest expense will be the trailer you will need to get your boat to the water.
The blue area in the photos will give you some idea as to where the glass is applied. The structural integrity is actually improved and you can keep doing mods as needed. #1. get the wrinkles out. #2. build a glass nose to slip into the pocket. #3. when you wrap the glass transom up the back you can build it right up against the original . The whole thing will tighten up when you inflate the boat. #4. The most important step is to make sure the inflatable floor has no air leaks. Launch and enjoy!
If you can't have fun on the water - stay on the beach!!
Tried to upload some descriptive phots to the boatbuilding gallery but am not sure if it worked. Where's the FTP when you need it?

[gonzo]

How do you attach the bottom to the tubes? I don't understand where the seam is. Have you done it or is this just your opinion?

[Windy]

how the bottom looks , note it is joined to the tubes.

[Windy]

can't get the photo(s) to upload?
So sorry!!!

[Windy]

One more tryhttp://members.shaw.ca/jamiedance/softy.html

Hope this works!!

[gonzo]

My question is if you have actually done it. I don't see a shell in your pictures.

[Windy]

Yes I put a shell on a 15 foot soft bottom boat. It was really easy and did help with the performance. I didn't bother with a rigid floor because itwasn't needed. I never bothered to take photos because there was no need.

The photos you are looking at is some old junker I found on the internet. Was trying to illustrate how easy it is.

Personally I wouldn't do a 20' soft bottom boat, they are too big and clumsy. Up to 14 or 15 feet works fine though.

As gonzo says, if the glass bottom isn't attached to the tubes, don't you have problems with abrasion?

Don't you get water in between the hard bottom and the soft floor?

I have no experience with a modification like this to an inflatible, but if the bottom is only pressing against the tubes from the bottom side and not following their curvature all the way up or sealed to them with adhesive, it seems (to this unexperienced reader) like the 'open' joint secured by tube pressure alone could be a recipe for disaster in rough seas...

Finally, if you lay up a rigid hull on the inflatible, does the heat from the fiberglass curing not hurt the inflatible?