1988 Bluefin-sportman has cracked ribs

[57sailplane]

i just got a 18 foot bluefin sportsmen i am redoing and pulled the whole floor out including foam and stringers.

what i found was 4 of the ribs have a crack were the the stringer is riveted to them. i am pretty sure this problem occurred from the trailer as the boat is not properly supported by it. most of the support is were these cracks occurred.

the ribs are half round with flange on both sides. the flanged areas are not cracked but the half moon areas are.

junking the boat is not an option. so how do i go about fixing? do i need to have these areas welded?

one other thing that came to mind is this boat has the usual ski storage area in the middle between the stringers. this was open. as i am planning to rebuild as a fishing boat i am planing on filling the center area with foam.. do you think this will help add strength to keep the ribs from cracking again.

thanks guys

later Andrew K

 

[jspano]

Re: 1988 Bluefin-sportman has cracked ribs

any pics... welding sounds like an option. if you are thinking of poured in expanding foam and its an alum boat think again

 

[Stratosman86]

Re: 1988 Bluefin-sportman has cracked ribs

Weld the cracks and "NOODLE" it!

Darren

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

any pics... welding sounds like an option. if you are thinking of poured in expanding foam and its an alum boat think again

why?, thats what was in it, the expandable poor in foam.. is there a problem in using it?

please elaborate..

thanks Andrew K

 

[ezmobee]

Re: 1988 Bluefin-sportman has cracked ribs

For cracked ribs I would definitely have it welded.

We've seen some corosion in aluminum boats due to poured foam. Not sure if it's the foam itself or whatever the foam traps against the hull. Most of us have been replacing our foam with the pink/blue construction sheet foam or pool noodles.

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

oh,

seems i can be of some use to the rest of you. since i tore my blue fin apart i found this pored in foam, and guess what they did and i wondered why and now i have my answer. they put down a thin piece of plastic like a drop cloth you buy at walmart. the thin stuff like a trash bag. they must of done this to keep the foam from corroding the aluminum or making it so the bottom can drain between the foam and hull.

since i am wanting to use the foam as a structural substance i will be putting it back in with the plastic liner. good thing i asked questions on here..

if you think this is still a bad idea please let me know. as i don't want to have this turn out badly after going to all this work and money.

thanks Andrew K

 

[geeco1]

Re: 1988 Bluefin-sportman has cracked ribs

Andrew,

The poured in foam does not add to the structural integrity of that hull. I also have 1988 Bluefin Sportsman and I just re-did mine about a month ago (see resto thread in my signature below). Mine also had the thin plastic sheeting around the foam, however, I don't think that this was to prevent corrosion. I think that the plastic was used to help control where the foam expanded to and to help keep it from sticking to the hull. My foam was soaked and weighed in at a couple hundred pounds. I replaced it with the blue sheet foam from Lowes or HD. The consensus on this board is that poured foam does not belong in an aluminum boat except on a few RARE occasions.

First thing to do is fix the trailer. Do you have any pics? Weld the ribs after that. The stringers will seem wobbly until you get the floor on. As an added precaution, I ran a thin piece of strap aluminum across my stringers and riveted it to the ribs on each side. Place your plywood on top of that and screw down. This will give you a solid deck.

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

hmm,

first i mean no disrespect to anyone. i am just trying to gather info to get the best outcome.

thanks for the recommendations on the trailer geeco1 i hope my boat turns out at least half as good as yours. you are defiantly correct. i went and looked at the trailer again. right now the boat is sitting with air gap between the hull and the back end of the planks. when i released the wench the front of the boat came up so right now all weight is on the front end of the planks.. not good.. so adjustments are going to be made..

as far as the foam. well i am going to be one of those contrary to this forum.. i have read others on here go with the noodles and blue foam because of drainage but this thing had the poor in foam in it and it drained just fine. this boat sat for 10 plus years with no cover.. being used in the summers.. so the foam was water logged all the time. guess what the foam was dry.. so dry it broke apart when i threw it out of the boat. it was still lite in weight. hardly any moisture at all. oh and by the way when i removed the rotted floor and foam the boat became much flimsier.

i have a lot of experience in the RC airplane world and many of my gliders have a wood sheeted foam core wing.. the strength is not from the sheeting and its not from the foam its the combination.. see if the wing was hallow it would fold because the sheeting would bend.. now if the wing were just foam it would crack and break apart due to lack of tensile strength..

i no from my experiences from my planes that the foam will add huge amount of strength to my boat..

i am not trying to start an argument but come up with a better solution to my problem.

the plastic sheeting will resolve the foam against aluminum corrosion chances..

now i think i have an idea for the drainage.. i will be doing the pouring in segments so i am thinking of putting a piece of 1/4" rope in between the ribs with ends sticking out. i will use masking tape to hold them in place loosely.. then lay the plastic sheeting over the rope then poor the foam. once the foam is cured i will pull the rope out and wallah drainage tubes. i will defiantly do this on a small compartment first to see how hard the rope pulls out. if the rope rips the plastic it will not matter as the foam will not be against the aluminum in that area..

anyways. i will take all your advise to heed.. please let me no if there is anything else i should be aware of..

later Andrew K

 

[geeco1]

Re: 1988 Bluefin-sportman has cracked ribs

Andrew,

No argument taken. That's what makes these forums great. Each person can give their input and ideas and each person can do what they want to their boat.

There is one thing that your are forgetting.......... pictures We all LOVE pictures.

Good luck with the restore and feel free to ask questions.

 

[ezmobee]

Re: 1988 Bluefin-sportman has cracked ribs

Well I will say that if there was ever an aluminum boat that required foam for structural support....it would have been a Spectrum Blue Fin

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

point well taken ezombee. lol.. ya she is pretty flimsy being all gutted.

i will definatley take some pics.

i have yet another question. the plywood was rotted and the edges were the rivets were are large holes now. i was going to use the old plywood as a guide for drilling the wholes but the outer ones are huge..

i want to put the new rivets in the old holes in the hull correct or do i need to drill new ones.. the holes are in the ribs. the other thing is i no they make a rivet washer.. can i drill the hole in the plywood larger and use the washer? or is this a bad idea? i figured if i have a bigger hole i will be able to get the rivet back in the original hole in the rib. or will this weaken the rivets?

thanks again for all your help andrew K

 

[geeco1]

Re: 1988 Bluefin-sportman has cracked ribs

I just drilled new holes on mine. Sometimes I would hit the old hole, sometimes not.

The rivet washers are designed to go on the end of the rivet, not the head. They are typically not any bigger than the head.

If you are using anything thicker than 1/2 plywood on the floor, you may not be able to find rivets long enough unless you special order from someplace.

In my boat, the back two sections were basically rectangular. I believe that each was around 61 inches or so. For those I did not need a pattern. for the front two pieces, where the bow starts to come together, I just measured and lofted the arc on the plywood. It was real easy to do and I can give you directions if needed.

I am really confused about a couple of your comments. You are saying that the boat is real flimsy when gutted???? Mine was rock solid. The only thing that I had to stiffen was the stringers, and that was done with a single aluminum strap. I was able to walk on my bare hull, climb in/out, etc with no flex. And I'm 260lbs. So I don't understand why yours is flimsy. Is something else going on with it??

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

i guess i over exaggerate.. its a lot flimsier then i a what think it should be. by gutted i mean the stringers and all are removed leaving the hull and ribs. it has other issues up top.. i am not sure what the area is called at the edge of the hull that is like 5 inches wide.. i would call it the lip or something but were this start to curve inward around the dash area, it is pop riveted together on both sides of the boat. well most of these rivets are gone on one side adding extra flimsiness. i am sure after i get it all back together and riveted she will be strong i hope.. the flimsiness is not like a noodle just i do notice a difference now that the floor is out.

thanks for the remarks on the rivets. i will have to do some research on these long ones as it had 3/4" ply in it and thats what i am putting back in.

later andrew K

 

[geeco1]

Re: 1988 Bluefin-sportman has cracked ribs

Ok. That makes a little more sense.

The top edge, by-the-way, is called the gunwale, pronounced "gunnel" as in tunnel.

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

ya,

as i said i hope mine looks at least half as good as yours. my boat is beat, and beat hard. hope she comes back together.

i just found the rivets at mccaster carr..

any other suggestions let me no as i am sitting this day out. it is 103deg out right now.. thats just to dang hot. lol.

laters Andrew K

 

[Stratosman86]

Re: 1988 Bluefin-sportman has cracked ribs

I bought my rivets at McMaster Carr as well. The 1" grip 3/16 rivet worked great in my Starcraft. My floor is 3/4 sealed with epoxy and I just popped a chalk line in line with my stringers and they pulled down nice and tight. I also marked my ribs on the side of the boat before I layed the deck down and riveted there as well.

Darren

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

so if i mark the side of the hull for the rib hole then write how far away it is form the side, then maybe i can hit the mark. do you guys see any reason i can not drill the plywood holes biger and use an aluminum washer. please let me no.. as far as the stringers i will just drill new holes. the reson i dont want to drill new holes into the ribs is there is so little material.. any ways if i must drill new holes into the ribs i will..

later andrew K

 

[geeco1]

Re: 1988 Bluefin-sportman has cracked ribs

Be careful as the washer will make the rivet head stick-up a little. Without the washer, the rivet head is ever-so-slighly pulled into the wood and the slightly rounded head leaves nothing to stick-up or catch on things.

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

thanks geeco1,

i was just thinking of using the washers on the outer edge at the sides of the boat were the ribs come into contact with the deck..

so if there is no reason i should not use the washers, this is probably going to be the root i go..

later andrew K.

 

[57sailplane]

Re: 1988 Bluefin-sportman has cracked ribs

hey guys,

i got the boat cleaned up pretty good now and am getting ready to adjust trailer. i found somthing i am not sure of and kind of wories me. on my boat like some others there is a 2 foot bay or aluminum area the width of the boat right in front of the motor atached to the transum. well the screws are loose and the aluminum is coming loose from the transom not real bad but i can see a gap in the seems. like i said this boat is beat pretty hard. also the deck plywood back there was solid and not rotted just surface wear. so how do i no if the transom is rotted, the motor has no play and if i pick up on the lower unit the boat begins to rise with no movement of the transom.. see i am worried as i am writing this to say there is nothing wrong but actually i dont no.

so do i worry about it or what. of course i am going to tighten the screws.. let me no what you guys do as the transom is totally covered in aluminum. also the area that is normaly below the water line of the transom is not thick its just one layer sheet aluminum. above the water line it is thick. anyways

thanks for your help

later andrew K