Airboat Hull

[Full Curl]

Greetings - new member here. I am interested in building an airboat hull. I am looking at an 18X8 boat. I recently completed an 18' driftboat using plywood and frame construction.

So, my question(s) are:

Plywood core or something like dyvinicell? Recommended thickness?
If I plan to attach 3/8" thick UHMW to the bottom, is there a need to go 'hi-tech' on the laminates? Kevlar, carbon, or just plain glass?
How can I attach the UHMW? The only way I know is w/ mechanical fasteners. That means hundreds of hull perforations. Do you just seal those with 5200? I was able to get some 'ionized' UHMW powder that I mixed in the resin for my driftboat...while that helps with some abrasion issues I don't think it does a thing to distribute impact loads

This boat WILL hit numerous rocks while in use. Most airboats up here are made of aluminum (3/16 to 1/4 bottoms). Since I don't know how to weld aluminum...and have some (limited) knowledge of constructing with epoxy, I thought I would give it a try.

Thanks in advance for your input.

[tunnels]

Originally Posted by Full Curl

Greetings - new member here. I am interested in building an airboat hull. I am looking at an 18X8 boat. I recently completed an 18' driftboat using plywood and frame construction.

So, my question(s) are:

Plywood core or something like dyvinicell? Recommended thickness?
If I plan to attach 3/8" thick UHMW to the bottom, is there a need to go 'hi-tech' on the laminates? Kevlar, carbon, or just plain glass?
How can I attach the UHMW? The only way I know is w/ mechanical fasteners. That means hundreds of hull perforations. Do you just seal those with 5200? I was able to get some 'ionized' UHMW powder that I mixed in the resin for my driftboat...while that helps with some abrasion issues I don't think it does a thing to distribute impact loads

This boat WILL hit numerous rocks while in use. Most airboats up here are made of aluminum (3/16 to 1/4 bottoms). Since I don't know how to weld aluminum...and have some (limited) knowledge of constructing with epoxy, I thought I would give it a try.

Thanks in advance for your input.

Hi
Impact you need A Balsa core and woven glass with A good woven Kevar on the outside of the bottom.The gelcoat on the bottom needs Silica sand and carborundium powder mixed in it to slow down the wear of mud and sand etc .Thickness id be using 3/4 inch balsa stuck in with core bond . ! I would also use Vinylester resin to make the hull and everything else like the deck and anything else as well .
To spray the gel coat you will need to use a pressure pot system . Never having seen one of these boats does it have a small keep or small runners along the bottom on the outside and a wearing strip ? ok seen what they do and where they go but dont have anything like it here in New Zealand .
The silica sand and carborundium in the gelcoat is what i used in surf boats that get draged along in wetsand at the beachs and it almost comlpetely stops the wear through . Kevlar has really good inpact strength but it needs good resin (vinylester) to hold it in place and not just shatter and let go .

[Full Curl]

Thanks for the reply.

For the botom, I was thinking of a flat section (say 2') and then putting a minimal deadrise of 2-3 degrees.

Not sure if I follow on the additives on the bottom - I was planning to put 3/8" UHMW sheet on the bottom. Are you saying to use the additives too? I like the idea of the UHMW as an 'active' procectant rather than resin additives as a 'passive' protectant...maybe I have the wrong idea though. If I go the UHMW route, any thoughts about sealing the hull perforations w/ 5200 sealant? Any other ideas?

Also, thought kevlar had high tensile strength, but compressive strength was about 30% of tensile. So the kevlar should be on the inside or outside?

[tunnels]

Originally Posted by Full Curl

Thanks for the reply.

For the botom, I was thinking of a flat section (say 2') and then putting a minimal deadrise of 2-3 degrees.

Not sure if I follow on the additives on the bottom - I was planning to put 3/8" UHMW sheet on the bottom. Are you saying to use the additives too? I like the idea of the UHMW as an 'active' procectant rather than resin additives as a 'passive' protectant...maybe I have the wrong idea though. If I go the UHMW route, any thoughts about sealing the hull perforations w/ 5200 sealant? Any other ideas?

Also, thought kevlar had high tensile strength, but compressive strength was about 30% of tensile. So the kevlar should be on the inside or outside?

Kevlar is abrasive resistant and needs to be on the outside, as for tensile strength no it stretchs a mile and will pull out of the resin if the resin is not good enough to hold it .what are the hull perforations you are refering to ???

[Full Curl]

The UHMW comes in sheets and about the only way to attach it is w/ mechanical fasteners as nothing will stick to it. Sure, there are people out there that have bonded a layer of something to UHMW that allow you to use epoxy, but I have heard of mixed results. The common way I have seen to attach it is with machanical fasteners, but they are typically through the hull perforations. Some use elevator bolts, others use countersunk bolts. As with many things with boats (and life) there are trade offs. The UHMW sheet is pretty bullet proof and distributes impact forces well. But the weak link is the many fasteners and keeping those sealed. UHMW moves quite a bit due to thermal issues. I was thinking that maybe using a sealant like 5200 would work to seal around the fasteners...maybe 5200 w/ a hypalon washer on each side...

My goal is to try to build a boat out of composites that will be just as durable as a conventional aluminum hull, but hopefully lighter. Plus, my labor for this type of construction is 'free'...but I don't know how to weld aluminum .