Boat Repair If You Dare

Inland paddling
Roboater
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Boat Repair If You Dare

Post by Roboater »

Posted: Fri Apr 25, 2008 8:43 pm Post subject:

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This was originally a reply to the chap with the holed Jackson but i thought i'd stick it on as a fresh posting.

I bought a cheap burn on here a while ago with a five inch split under the seat.
Fixed it with two, eight inch by four inch pieces of eighth inch thick aluminium.
I drilled a series of holes through both plates, used one as a template to mark the boat then,( BIG GULP !)drilled through the hull. Fourteen holes later and all I had to do was bolt the whole thing together, one plate inside and one on the bottom, using short roofing bolts (dome topped for a low profile) and loads of sealant.

The pressure of cranking up the bolts, plus the sealant has left a totally waterproof and very tough repair.I've used it lots and it's the mutts nuts.
It's fine until I start scraping rock.Then the bolt heads do catch a bit but it's horses for courses I guess.
I have a mate who's a good metal worker who's gonna knock me up a new version with studs instead of bolts.This should give me a flush profile and reduce the shallow water problem to a minimum.
Find an old plastic boat to try it out on first though as drilling fourteen holes in the bottom of the Burn was a bit nervewracking.

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naefearjustbeer
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Post by naefearjustbeer »

Hmmm what about a nice titanium plate on the outside so when you do some of those fancy out of the water rock slide type thing you will emit a shower of sparks. Just like the bikers with the titanium studs in the knee sliders. Would make rocky seal launches more interesting.

Roboater
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Post by Roboater »

Yep titanium would be lightweight, strong and spectacularly sparky.
A bit expensive and tricky to get your hands on though I think.
If anyone knows where I might pick some up drop me a line.

jenx
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Post by jenx »

Do you find that you're getting stress concentrations around the extremities of the alu plate? ie would that cause the plastic to fail there instead of the crack yoiu've just covered up? I guess you've used fairly thin sheet though so that's not an issue. Just wandering as I'm thinking of trying it on a broken boat now as well!

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jimkennedy
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Post by jimkennedy »

Photos?

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Big Henry
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Post by Big Henry »

Imagine flying down the Llyn Briane spillway, a trail of sparks flying out from behind! You'd have to do it in the dark for better effect, of course!

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TheKrikkitWars
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Post by TheKrikkitWars »

Big Henry wrote:Imagine flying down the Llyn Briane spillway, a trail of sparks flying out from behind! You'd have to do it in the dark for better effect, of course!
Imagine doing it in an all-alu Grumman canoe!
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clarky999
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Post by clarky999 »

The heat from the friction would probably cook you...

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TheKrikkitWars
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Post by TheKrikkitWars »

clarky999 wrote:The heat from the friction would probably cook you...
First I thought that the canoe would succumb to hot shortness and become little more than a cloud of hot metal vapour, then I thought about sliding down pit tips on thin corrigated alu sheeting (not that I ever have) and the canoe would just wear away leaving a slivery trail.
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clarky999
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Post by clarky999 »

What's a pit tip?

Roboater
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Post by Roboater »

Hi Jenx. I've had no troubles with stress fractures etc around the edges of the plates (so far) and am really pleased with the results of the repair. I was a little concerned about the edges of the plate catching on stuff but so far so good.
Ideally i'd like an eighth of an inch thick piece of titanium and chamfer the
edges to reduce the risk of it catching on rocks. Welded studs rather than bolts has got to be the way forward but for now i'm going to grind down the dome heads on the coach bolts to give a reduced profile.
Reckon i'll need to put lots of water in the boat to prevent heat build up and melted plastic.

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Post by Roboater »

Hey Jen. I forgot to add, when/if you try repairing your boat , could you let me know how you get on and what the results are?
I'd be interested to see how others get on. I reckon this is a cheap,strong and durable way of repairing plastic boats but am very interested to see what others think.
It could be the only lasting repair for thermo set plastics (High density, cross linked) that i can think of, but i'm no expert.
All the best .
Rob

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RichA
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Post by RichA »

Hi Rob, it was actually me posting on Jen's account t'other day. Sorry Jen! :p

The other alternative method a mate suggested was to source a piece of plastic about 8" square and put it in the oven until it was soft. Heat the hull of the boat at the same time. When they both get a bit tacky slap them together and use a carpet roller etc to bond them. Then plastic weld around the edge of the patch. This would negate the risk of the edges catching on rocks and the split would remain waterproof even if it opened up again due to the size of the patch extending further outwards than the split itself.

A simlar effect has been done before using a cut up plastic milk bottle and some roofing tar!

dwbald
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Thickness off metal plate

Post by dwbald »

Hi Roboater, What was the thickness of the metal plate used?

Just thinking if it was thick enough you could counter sink the holes and use coutersunk screws. chamfer the plate edges and haypresto low profile with no bolt heads...

For the inside cut the screws, or buy exact length, with enough thread to fit dome capped nylock nuts. low profile and smooth so no nasty gashes on back of legs.

Go ask your local nut and bolt specialist shop (Not B&Q etc they are very limited in there stock) look for the place that specialises in fixings They will have a bewildering choise so ask for there help you will be suprised what is on the market...

Cheers Dave B

Just remember messure twice cut once.

Roboater
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Post by Roboater »

Rich.
Sounds like a version of plastic repairs that could well be viable and durable. I don't know if it would work with thermo set plastics.The low service energy is always going to be a problem with plastic and my understanding is that the problem of welding magnifies greatly with thermo set. The size of patch you suggest sounds similar to the aluminium repair I used. I've had no problems so far with the edges catching and the forces involved due to the bolts keep the seal incredibly strong and watertight. The mastic sealant does the rest.

Dave.
I've used aluminium plate an eighth of an inch thick.
I've discussed the countersunk screw idea with mates but not tried it yet. My concern was about the raised profile that would be needed to accomodate the countersinks. I'm sure that a good metal worker would be able to give a more informed response than mine.

I still think that the hull plate would be the best answer, made with studs fixed to it, negating the need for the extra thickness needed for countersunk screws and avoid having domed bolt heads showing as I have at the moment. I'm no engineer though so expert advice might be useful if you have it available.
I think this would give a neat, practical solution and would probably look a lot nicer than the terminator/cyborg thing i've got going on the hull of my boat right now.

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Ross W
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Re: Boat Repair If You Dare

Post by Ross W »

Roboater wrote:
Fixed it with two, eight inch by four inch pieces of eighth inch thick aluminium.
I
so in total you had 16' of extra aly on there?
Dartmoor / Plymouth based
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dwbald
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Post by dwbald »

Just looked at 1/8 inch plate think counter sunk wouldn't work on plate that thin. Would need more like 1/4 inch.

At the moment do you have the bolts head on outside of boat or inside? I assumed outside with nuts in cockpit floor. was thinking that on inside once plate fitted for added protection you could glue thin foam sheet. Just an idea.

Im not a welder by trade but we have at work so will ask his opinion on monday, think you would need thicker plate for studs to get good weld on the plate. Alos aluminium is a bugger to weld and needs specialist welder...

Need to go find broken boat to play with now see what you have started lol

Cheers Dave B

Roboater
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Post by Roboater »

Hi Dave.
The nuts are on the inside of the boat and dome headed bolts outside.
I've a mate who's a coded welder and he assures me it's a straight forward job for him and 1/4 inch aluminium is fine to fix the studs to.

All the skilled guys i've spoken to say that titanium is the best stuff but its
a problem finding the right size and thickness.

Maybe i should try the internet!!!!!!!!!

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RichA
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Post by RichA »

Rob, I don't think there will be any worthwhile advantage of using titanium over something like hardened steel. Ti is also much harder to weld succesfully. The specific strength of Ti is much greater, but for the amount of material you are using the weight saving would be negligable compared to steel or even alu. Also, the increased hardness is probably not worth the money, but that's just my opinion.

Welding studs onto 1/4" Alu-sheet would be fine, but I thought you were using 1/8" sheet? That might be a little harder. Still possibile, but more likely to get cracking around the welds as the weld penetration will have to be much less. Still, if you have enough studs on it you should be fine. Good luck - I'd be interested to know how it holds up. I think we're going to have a go at the plastic welding of a patch using the oven and several blow torches, but we'll give the metalwork a go if that fails :-)

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Ed Lefley
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Post by Ed Lefley »

I knew someone who used this (or a similar technique) for fixing his dagger boat (IIRC).
It did work, but we always let out a slight groan when we saw his name on a trip list as the boat had leaked on previous occasions.

I think that there are a number of issues around this technique; 1 of them is ensuring that you get a good seal on the fix, 2 making sure that the screw heads are not a snag or cut risk for those around the boat (in or out of the boat)

How you avoid it snagging on bony rivers or those with a slide on (I've got in my mind something like the Upper Ardeche in places, or the weir on the Wenning) is a bit more of a challenge I expect.

Good luck with it though none the less, I'm sure Pete the Kayaker may add more to this as he also paddles with the guy above

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Post by Roboater »

Hi Ed.
I've had no problems at all with leaks. Plenty of mastic sealant on both plates and in all the bolt holes took care of that. As for getting hooked up in shallows...Yep I can definitely tell when there's contact but it's not severe.

When things are that shallow everyone else tends to be scraping too.
Perhaps when its that shallow we should be thinking of walking round.
Long paddles over boney shingles and dry rock/ boulder gardens isn't my thing to be honest. I like my rivers with water in them. When they are empty I can always go off and do something else.

No worries at all re sharp edges and the danger of snagging skin.Just need to use common sense when choosing bolt lenghts etc.

The reason for considering titanium was as a final solution that wouldn't rust etc, as opposed to needing extra strength, where steel might well be a problem over time, stainless or otherwise. That said, the ease of the repair with plates (it was VERY easy) might make stainless steel the thing to go with. If there are any rust issues over time (doubtful) replacing it would be relatively straightforward.

What the plates did for me was get me a Burn for £200 that I now use as a very comfy coaching/river leading boat, that'll run beefy white water too without the worry of the repair coming undone.

Really grateful for all the feedback and interest guys.Wasn't expecting my post to have ellicited such a response but it'll be interesting to see how others get on shouold they choose to try it out.

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MassiveQueen
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Post by MassiveQueen »

This was a repair method employed in the past by Fred the grumpy so and so who used to run Southampton Uni's Boathard, I think he thought about it a whole lot less than you have and the results were less than satisfactory!

I think that the way he assessed whether a repair was sound or not was based on the theory that if you can't see a hole then how can there be a hole!
Older, no wiser

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TheKrikkitWars
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Post by TheKrikkitWars »

clarky999 wrote:What's a pit tip?
Or Slag Heap... its a big steep sided hill of spoil from a coal mine, the biggest in our area is about 400m high and a 50 degree gradient... fun, fun, fun.
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dwbald
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Post by dwbald »

Roboater wrote:Hi Dave.
The nuts are on the inside of the boat and dome headed bolts outside.
I've a mate who's a coded welder and he assures me it's a straight forward job for him and 1/4 inch aluminium is fine to fix the studs to.

All the skilled guys I've spoken to say that titanium is the best stuff but its
a problem finding the right size and thickness.

Maybe I should try the internet!!!!!!!!!
Hi Roboater,
Talked to the welder at work said you couldnt weld steel bolts to ally thought you couldnt but best to ask the experts. He did however suggest riveting the plates as this would give no profile problems.

More food for thought
Cheers Dave B

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RichA
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Post by RichA »

Oh yeh, I assumed you were using alu bolts on the alu sheet. You're right, you can't weld alu/steel together. Well, you can but it's a right mess and won't last long!

Alternatively weld alu studs to the sheet and thread the ends to recive a nut in the boat? But then you have the problem of steel nuts on alu threads in a wet environment, unless you can source alu nuts as well?

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ChrisT
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Post by ChrisT »

I reckon you could get away with rivetting the plates together, if you use monel rivets. Does mean you need a decent rivet gun though.

Good effort on getting a working Burn for £200 anyway!

dwbald
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Post by dwbald »

Not come across ally studs think ally isnt strong enough to keep a thread. Its why ally engine blocks have steel thread inserts.

Think if there are ally studs steel nuts would just rip the thread straight of under any decent torque...

Cheers Dave B

dwbald
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Post by dwbald »

ChrisT wrote:I reckon you could get away with rivetting the plates together, if you use monel rivets. Does mean you need a decent rivet gun though.

Good effort on getting a working Burn for £200 anyway!
Could you not use cold rivets a little auckward to get a good base to strike against
Dave B

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ChrisT
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Post by ChrisT »

They use aluminium bolts for non-structural parts on motorbikes but I agree that they probably wouldn't be suitable for this application.

Stainless steel fastenings and plates is probably the way forward I would have thought...
dwbald wrote:Could you not use cold rivets a little auckward to get a good base to strike against
Dave B
I was thinking of pop-rivets from the outside (could also countersink the plates a bit to get them nicely out of the way of nasty rocks)...

dwbald
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Post by dwbald »

ChrisT wrote:They use aluminium bolts for non-structural parts on motorbikes but I agree that they probably wouldn't be suitable for this application.

Stainless steel fastenings and plates is probably the way forward I would have thought...
dwbald wrote:Could you not use cold rivets a little auckward to get a good base to strike against
Dave B
I was thinking of pop-rivets from the outside (could also countersink the plates a bit to get them nicely out of the way of nasty rocks)...
Pop rivets are notiriously difficult to get right, we have real trouble reseating ally body panels at work. Pop-rivets can leave a looser fit, not giving enough force pulling the plates together. Thinking it would work as these plates are just a simple sandwich.

Cold rivets would work better but it would be difficult to get a strike plate on the other side

Think I would try the pop-rivets first then check it out...
Cheers Dave B

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