Hog back canoe

[ozarkpaddler1]

Ok, this may be a strange question to all of you seasoned boat builders but it's got me perplexed. I am in the middle of building a strip boat. I've fiberglassed the exterior of the hull, removed the hull from its forms and glassed the interior. With the boat free of the support that its forms provided and turned upside down on saw horses I notice that the hull has a noticeable "hogback" that was not there when the boat was still on the forms and strong back. I have to assume that the bottom of the hull is sagging in due to the lack of support although I cant say for sure because I can't tell if the curve remains in place when the hull is turned right side up. I should add that no hog was present when the boat was on its forms and it had a perfectly straight string line until the the forms were removed. Question is --- is this common? What caused it? Should I fix it or what's the best way to remedy this issue if it's a problem? What would you guys do? Guess I should have mentioned, the boat is a 17 and a half foot solo with pretty extreme thumbhome, less than 30 inches wide, quarter inch cedar strips (although pretty heavily sanded) 6 oz E glass outside,
4 oz E glass inside.

Thanks John R

 

[yellowcanoe]

Did you add spreader thwarts?

 

[memaquay]

You mention that the inside is already glassed. How did you support the canoe when you were glassing the inside? On one of my very early builds, the bottom of the canoe was resting on the strongback when I glassed the inside. The result was a permanent hog. On another canoe I built, one with very little rocker, the design plans had messed up the stems, so that they were slightly higher than the rest of the canoe. Result - hogged canoe. Once you have glassed both sides, pretty hard to get out.

 

[ozarkpaddler1]

No Yellowcanoe, I have not added thwarts, gunnels, decks or seat yet. Basically just a bare hull right now.

 

[ozarkpaddler1]

Memaquay, the boat was sitting in two strap cradles situated about four feet in from the stems when the interior was glassed. Probably should mention that the boat has zero rocker.

 

[Guest]

On a positive note; I have had 2 canoes made with what some would called "hogged hulls" and they both paddled well.

 

[deerfly]

Mem is correct. I think this is something that you rarely see discussed, but should be for those that may not recognize the potential problems from hull distortion as you add back rigidity after removing the hull off the forms.

In your case I would say gravity on the hull in the straps did not agree with the hull contour on the forms. So after laminating the inside the hull became more rigid but did not follow the same shape as the forms.

To avoid or minimize this distortion you need to jig up some supports that follow the female shape of the male station forms before laminating the interior. Not all of them, but enough to preserve the keel line/rocker gunwale separation from the opposite side, etc. I would say 3 supports at a minimum, 4 probably better, but longer designs may warrant more support locations. That way when inner layer of glass cures you're retaining the correct hull contours.

If the distortion is bad enough to alter the performance or use to your tastes I would cut those female supports from your male forms, jig them up true at the same offsets, then place the hull down into them. If you have the stomach for it, sand, grind or peel the inside layer of cloth off the wood. You could start where the hull is deformed and work out from there without having to do the whole hull. Then add stronger layer of cloth to the inside. Either the same 6oz you used on the outside or consider 4 or 6oz s-glass, 5oz kevlar, or 5.5 oz carbon innegra. If you sanded down or removed the 4oz cloth this should get it correct again. If you didn't grind down the inside the stronger fabric may still help counter the distorted tension enough to get some of the hog back out at the expense of another 5lbs or so of weight. Either way you may need to hot glue or screw the hull to the female forms in places to hold it down and fill them afterwards.

As a last resort Craigslist is full of willing canoe buyers that won't care about the hog back

 

[Cruiser]

How long between the outside glass application and inside? I have read about glass distorting the shape as it cures if it isn't counter balanced by the second layer ... not usual but I believe it can happen.

A couple of pics would be worthwhile.

Brian

 

[ozarkpaddler1]

Well deer fly the concave curve appeared as soon as the hull was removed from the forms so I don't think it has anything to do with the support or lack there of once the hull was flipped right side up. There again cruiser the hull did spend a couple weeks waiting for it's inside glass layer but the curve appeared as soon as it left the forms.

 

[memaquay]

Out on a ledge here, but.......Were you using red cedar? Were the strips flat sawn or quarter? I was given a bunch of very dry red cedar once, where the strips turned out flat sawn. They had very little integrity, and after glassing the outside hull and leaving it to sit off the mould for a week or two, weird things happened. Strips cracked, the hull curled in on itself, it was a mess.

 

[Jim Dodd]

Ozark ?

Others are right, this isn't brought up a lot. And you are not alone !

There are a couple things that come to mind. First I agree, you probably won't notice any difference, unless you are really into Free Style paddling.

Was this a Stemless build ?

When you glassed the exterior, did you leave it on the forms to sand ! I do. Another thing I do, is leave the Center form, STRAPPED in, while I sand the Inside. Until I get to sanding the center.

Lastly, I have had this on a few earlier hulls. I have since modified my Stem forms, by cutting them a little lower. Something about the strips on the Stems, as they come together.

On your Next build, you might want to try this ! The stem form is set about a 1/4" lower then the end form, and lightly sand the leading edge of the last form.

 

[alsg]

So, does a hogback become an oil can when put right side up and in the water? When I built mine, I made three supports to hold the canoe while I glassed the inside. Basically traced the forms, cut the profiles, and covered the edges with foam rubber insulation. I think this is what deerfly was talking about. Here's a photo or two:

 

[memaquay]

My understanding of oil canning is different from hog back. A hog back is a permanent feature in the hull. A hull that oil cans might look perfect before it goes in the water, but due to the lack of rigidity in the hull, the water pushed the hull up. My poly canoe oil cans so bad that its like watching waves on the ocean. The bottom actually ripples. However, my strippers that were hogged did not oil can, they retained their shape once in the water. Clear as mud?

 

[Trevor Paetkau]

Forgive me if this has already been mentioned.

Have you put a spacer(s) into to ensure that the sheer adheres to its design beam? My first thoughts are that there is where the deformation starts.You'll be surprised at how the hull shape changes as you push/pull the center apart/together.
Second, what happens when you place test stations back into the hull. Does the hull conform? If not what happens when the hull is pulled/pushed into place? If the hogback still exists after trying both these options, the issue is beyond my ken ...

Good luck ...

 

[ozarkpaddler1]

Memaquay, yes the hull of this boat is made with western red cedar. I ripped the strips out myself and they are mostly quarter sawn but some are probably flat sawn as well. No other problems with deformation other than this hogback.

Jim Dodd - yes the build was stemless and yes I did leave the hull on the forms while I sanded and glassed the exterior. I can certainly see the value of keeping the center form in place while the inside is being sanded and I also like the idea of lowering the stem forms slightly. I'll be using both tips on future builds, wish I'd thought of those before I started this build for sure.

Trevor Paetkau - yes I agree the hull may change shape some as I add gunnels and thwarts. The hull is spread apart slightly now so probably my next step will be to put a few of the forms back in and then wrap a couple rachet straps around the hull and see what happens when I tighten them up. Hopefully that may restore the hulls shape.

I guess I'm probably not going to know for sure until I finish assembling the hull and I get all of it's supporting components in place.

Thanks for all of the input so far, great information.

John R

 

[Jim Dodd]

Hi John

Again it is a common problem, and after your response. Lowering the stem forms, and sanding the last form, before the stem, should will eliminate Hog !

I learned from experience ! The Hard way !

Jim

 

[PortlandBCS]

The increased angle of the strip joints at the stems makes more of a difference then I would have believed. Luckily my first build included a fair amount of rocker. The not-anticipated angle changed my rocker by a half an inch.

 

[Holmes375]

Ozark ?

Others are right, this isn't brought up a lot. And you are not alone !

There are a couple things that come to mind. First I agree, you probably won't notice any difference, unless you are really into Free Style paddling.

Was this a Stemless build ?

When you glassed the exterior, did you leave it on the forms to sand ! I do. Another thing I do, is leave the Center form, STRAPPED in, while I sand the Inside. Until I get to sanding the center.

Lastly, I have had this on a few earlier hulls. I have since modified my Stem forms, by cutting them a little lower. Something about the strips on the Stems, as they come together.

On your Next build, you might want to try this ! The stem form is set about a 1/4" lower then the end form, and lightly sand the leading edge of the last form.

Hey Jim. When you say, "lightly sand the last form", are you simply fairing it slightly to let the strips lay better on the lowered stem form?

 

[Jim Dodd]

Yes.
The edge of the last form, needs to be releaved, or lightly sanded At this form and really all the forms, except the center form, the strips ride on the edge closest to the stems. I always lightly sand this edge. It also prevents denting on the inside of the hull.
I know the pic really doesn't show this clearly.
Lowering the stem forms, and sanding the forms has worked for me !

Jim

 

[Holmes375]

Thank ya, sir.