Best fiberglass/epoxy for this application?...

[josh2000ford]

I have a 1952 herters yukon that I use for waterfowl hunting. I have a big " mud motor" so I have built floatation pods off the transom using polystyrene foam. Basically these give better floatation in the back because of the weight, and some performance, like planing out.

I built these 4 years ago and used uscomposites fiberglass and 2 part epoxy. It held up good over the years. Obviously the occasional repairs due to ice, but this past season I found big cracks on the bottom of the boat, where the pods meet the transom. This boat does see a lot of mud flats, cattails and other objects you find in a wetland. I plan on flipping the boat and repairing this and am wondering if theres a better epoxy for this application. I do plan on giving the whole bottom a coat of just epoxy. The boat does sit in the water for 3 months out of the year, from 100 degrees to 0 degrees!

here are some pics of the pods







thanks,
Josh

 

[colbyt]

Re: Best fiberglass/epoxy for this application?...

I don't know about the epoxy.

I will offer a design option for your consider that might make the entire thing stronger. Instead of bolting them directly to the boat make a new transom board that mates to the outside rear of the existing transom. You should be able to better distribute the stress over a wider area.

Disclaimer: this suggestion is from someone who knows nothing about what you are doing but who does understand stress points.

 

[Bomber Goober]

Re: Best fiberglass/epoxy for this application?...

Delete

 

[Woodonglass]

Re: Best fiberglass/epoxy for this application?...

Is the boat Glass or aluminum?

 

[redfury]

Re: Best fiberglass/epoxy for this application?...

If the boat is aluminum, then you are going to have a hard time getting those pods to stay attached just using fiberglass and epoxy. you'd be better off building them as a detachable section, and then bolting it onto the boat ( create a back plate that attaches to the transom ) If the boat is fiberglass and you want to attach it to the boat properly, a coat of epoxy over the whole bottom will do nothing. As strong as epoxy is, it's nothing as a stand alone product in sheet form in comparison to being strengthened with fiberglass. If you are having problems with fiberglassing it to a fiberglass hull, then you need to run the fiberglass further into the hull and you'll want to make sure you are using enough glass thickness to have the strength and durability you are looking for.

 

[josh2000ford]

Re: Best fiberglass/epoxy for this application?...

Sorry, yes the boat is fiberglass. The pods were fiberglassed directly to the boat. This was glassed about 2 feet onto the existing boat. IIRC we did 3 coats. There has been no issues the with fiberglass or epoxy adhering to the boat, just looking to see if there was a better epoxy than the 2 part from uscomposites. I plan on putting a coat of epoxy on the bottom just for a little protection. Fiberglassing the whole boat would be a little too heavy!

 

[jbcurt00]

Re: Best fiberglass/epoxy for this application?...

If there isn't an adhesion problem between you're additional pod structure & the rest of the boat, I doubt the US Comp epoxy is the problem. The epoxy & glass you used isn't delaminating from the hull, correct?

IMHO, fiberglass & epoxy isn't exactly the problem, it just wasn't strong enough to w/ stand the forces & stress you're subjecting it too. Different areas on a boat hull are 'engineered' to withstand 'normal' forces that they will experience while in use. The cross section of the fiberglass hull may be 3/6" thick along the hull bottom, in general. But where the keel meets the bow, or at a chine, the fiberglass may be thicker. Across the stern, the transom glass may be thicker still.

Since you haven't posted the layup schedule you used, it would be helpful if you did. Perhaps the actual glass (&/or it's weight) wasn't sufficient. Using a light weight cloth or mat, may not have had enough structural strength. Using 1 layer of glass & epoxy followed by additional coats of just epoxy, may have also been insufficient. If you used 3 layers of 1708 fiberglass & epoxy, you might try 4 layers.

Adding a 'spar' that is integral to your pod & runs along the side of the boat may be enough to help overcome the stress of the water pushing back up against your pods (1st portion of my rendering).

Triangular shaped gussets above the pods may also help prevent the cracks from reforming. 2 or 3 gussets that extend from the transom to the back edge of the pod would be much better then 1 or small gussets that don't extend all the way back. (bottom part of pix)

I suspect that a combination of a better layup schedule, gussets & the spars would be the best way to prevent the craacks.

As I'm not an engineer, and haven't seen your boat in person, that ^^^ is all speculative at best.

 

[Woodonglass]

Re: Best fiberglass/epoxy for this application?...

What weight of glass did you use? How many Layers? How many Coats of Epoxy? Which Epoxy from USC?

 

[ondarvr]

Re: Best fiberglass/epoxy for this application?...

Adding a coat of epoxy to the hull won't do much except cost money and make it slightly heavier, it won't add strength or stiffness.