Starcraft Fishmaster Leak and Frame Repair?

[meerkat]

My 2001 Starcraft Fishmaster 176 started leaking badly from a number of rivets.

I pulled the deck only to find that I have cracked welds under the deck between the two front seats. I suspect that these cracked welds are allowing flexing that is causing my loose rivet problems.

There 5 structural members (stringers?) running fore and aft and 2 ribs that run side to side. The vertical stringers on each side and the ribs are welded in each corner to make a rectangular box. The ribs are then welded to the main stringer running up the keel. All of these welds (6 of them) are cracked (no separation but cracked right through).

I took it in to be repaired. They said re-welding would weaken the structure so they pop-riveted 1 inch aluminum angle brackets over the welds and tightened the loose rivets.

That worked for a short while but now, after 2 months the boat has more loose rivets than before and is leaking like a sieve.

Is this a flaw on this model of boat? Is there a way to fix it? Do I need to reinforce the frame and if so how?

I love this boat and would really appreciate any suggestions for a permanent fix.

 

[Gnarly]

Re: Starcraft Fishmaster Leak and Frame Repair?

could you post some pics of the damage?

A doubler with reinforcement (boxing it in) may be the solution however its hard to guess without something to go by. I think you may have something structural broken allowing the flex and progressive rivet failure or are you really pounding the boat? , it sounds like they may have just tried to stiffen it with angle and a more permanent better engineered solution is in order, welds don't handle vibration very well at all and riveting might be a better mousetrap for the repair, solids are better than blind rivets but both have their place, a good resource for this type of repair is a publication called AC43-13 1A/2B ACCEPTABLE METHODS,TECHNIQUES, AND PRACTICESAIRCRAFT INSPECTION AND REPAIR, it will cover anything from structural repairs to wiring and just about everything in between and should be available at your local pilot shop.

 

[meerkat]

Re: Starcraft Fishmaster Leak and Frame Repair?

I presume by boxing it in you mean fabricate a box to fit inside the box that already exists and rivet it to the existing box? I had thought of doing that - so great minds think alike.

I do not pound the heck out of the boat but I suspect that at some point it did take a hit that broke the welds. After that the whole structure of the boat was able to flex and progressively loosened the welds. So again - great minds think alike.

My thought is to build the box (with some reinforcing gussets?)- rivet it in and then go over every rivet on the hull and pound it tight.

I will take some pictures and post - good suggestion - I should have thought of that.

Thanks for the come-back - any other thoughts?

 

[Gnarly]

Re: Starcraft Fishmaster Leak and Frame Repair?

Meercat the only other thing Im thinking would be to add doublers to the hull (skin) at the attachment points to add a bit more strength and shore the load as well. Rivet choice is going to be somewhat critical and pop rivets arent going to cut it , the shear and tensile strength just isnt there and I'd suggest 5200 series solid rivets be used where you can and structural blind rivets where you cant, try and assemble everything with a quality sealant (pro seal 870 or PR 1422) available at aviall , it'll sure help with the rivets staying tight and sealed and helps prevent crevice corrosion.

Best of luck with your repair

 

[meerkat]

Re: Starcraft Fishmaster Leak and Frame Repair?

Okay - here are some pictures.

Diagram a.jpg is a diagram of the boat and the damage...
Boat Frame 1.jpg is a picture of the same thing looking towards bow..
Boat 2.jpg is a close up of Boat Frame 1.jpg. In this picture you can see the angle brackets pop-riveted over the welds into each corner and between the rib and the main beam up the keel. A picture looking towards the stern would show the same thing.

Do these change anything? Any further comments? Thanks for your help!

 

[meerkat]

Re: Starcraft Fishmaster Leak and Frame Repair?

...oh, I almost forgot. On the close up, the worst rivets (loosest) are the ones that join the vertical plate on the left to the bottom of the boat and the vertical plate on the left is warped (lost it's structural integrity?).

Also the two stringers that run up either side of the keel end just before the bow and butt up against the two other stringers that run up into the bow. Seems like a design flaw to me - this is a high stress area. I am thinking about how to join these in some way to reinforce the join area

 

[Huron Angler]

Re: Starcraft Fishmaster Leak and Frame Repair?

Have you considered just rebucking the rivets using a hammer and heavy piece of flat steel...then apply gluvit(avail here at iboats) to seams and rivets. The gluvit will seep in and is designed to flex with the hull yet remain watertight and people swear by it when persistent leaks are a problem in aluminum hulls.

Sorry to hear of your issues, good luck with the starcraft repairs.

 

[Gnarly]

Re: Starcraft Fishmaster Leak and Frame Repair?

Thanks for the pics , it looks to me like the forward left let go some time ago allowing the flex to loosen the affected rivets and finally pop the remaining welds.
The fix (just my thoughts)
how are your metal skills and tooling?

I think the problem here is a lack of transverse bulkheads you show two in your drawing that are tied in with welds and spaces fairly distant from each other, when the boat is banging in the chop with hull twist the attachment points are being stressed breaking the welds, I bet if you built a couple more bulkheads tieing them to your structural members in the forward compartment it would go a long way towards alleviating the problem.
First off lose the angle pieces they installed and get some larger (more surface area angles bent up to the correct angles and tie them in with closer rivet spacing (one inch and multiple rows) and structural rivets with either structural adhesive applied or at least sealant between the metal. Remember you want to bend them against the grain of the metal not with it (crack)
Fab a couple more transverse bulkheads, space and tie them into the structural members the same way and watch the angles and radius of your work otherwise you'll set up stress risers and it will crack on you in time. Construction paper and tape a prototype together. If possible use .100 or .125 5052 aluminum for the meat of the bulkhead and bend some .060 into angle on both sides to tie it all together in a sandwich riveted to the hull , the bulkhead and the structural longerons ( you'll need a shrinker / stretcher)I'll try and draw something up tonight and take a pic to forward to you. Study semi monocoque construction aircraft bulkheads or even wing ribs to skin attachment to get the jist of it.
If I was doing it I'd put some skin doublers in on the inside of the hull at the attachment points as well to shore the load.

You could box it as discussed before and it would accomplish almost the same thing but the stresses would still be localized, I think more bulkheads would work better and there would be less chance of cracking.
my .02

 

[meerkat]

Re: Starcraft Fishmaster Leak and Frame Repair?

Thanks for the very useful input and suggestions. Gnarly - if you get time to sketch your last ideas I would appreciate it but if not - I think I got it. My son-in-law has his own commercial refrigeration business and fabricates stainless for coolers, etc so he can help me with the fabrication of your suggestions. He keeps telling me to use stainless but I do not want to mix the two metals because of different rigidity issues that might cause more problems.

I am in the process of pulling all the decking, etc to get at the hull and all the structural members. From what I can see so far, the left side member is definitely quite badly bent! Probably the cause of all the issues.

Anyone know how the side decking is attached? The middle deck is just screwed down but the side deck is covered with vinyl so I can't see how it is attached. It looks looks like it is plywood pop-riveted to a plate and then to the structural member running fore and aft. The seat pedestals also seem to be attached to the plate. The plywood and vinyl is good so I do not want to damage it unless I have to.

Again - many thanks!