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Planning Surface

PostPosted: Tue Dec 15, 2015 5:33 pm
by thegammas
greetings all, this is a side thread to "bottom rebuild (prev 'at a cross roads)"

My boat has a hook (concave area ) at the stern which causes handling issues when I push it past half throttle (she's got a 100 HP after all!). My plan is to use marine filler to fair the garboards flat again on the planning surface section of the hull (the concaved areas are not too deep, maybe 3/8 inch at the max..

So the question is, on my 17 footer, how far from the stern forward is the planning surface?

Re: Planning Surface

PostPosted: Tue Dec 29, 2015 3:55 pm
by JoeCB
I see that no one has responded to your question, so I'm thinking that maybe we can kick-off a discussion. My guess is that the further astern the concavity the more pronounced the effect will be on handling. The worst condition would be for the "hook" to be immediately forward of the ransom. As for "how far the planning surface extends" , that will depend on many factors... loaded weight, weight distribution, hull condition, engine power, motor trim angle, etc. On my 17' Sea Lancer with 75 HP, most all the hull is "wet" even at planning speed.
On your question of "filler" to correct the hook, I have no experience, perhaps someone else here does.

Joe B

Re: Planning Surface

PostPosted: Wed Dec 30, 2015 12:10 pm
by LancerBoy
I have no idea. Sorry.

Andreas in Peshtigo

Re: Planning Surface

PostPosted: Wed Dec 30, 2015 7:19 pm
by thegammas
Thanks for chiming in Andreas.

The worst of the hook is right at the transom. It was caused by that all too typical mistake of leaving the boat on the trailer on roller bunks that did not extend past the transom, with an engine on the transom. I say this because when I bought it, that's how it was sitting on the trailer and you could see where someone had painted around the bunks. I was a complete novice when I got the boat, so didn't know what to look for or avoid.

On the FaceBook page "Thompson Boat Owner's Group", I got some feedback that, as Andreas says, that the length of the planning surface depends on many factors. I also got some feedback that fillers can work well to correct a hook.

Checking this and that with a long straight edge and taking some measurements, I think I can get the last 5.5 feet of the garboard panels flat and straight. Forward of that, the hook isn't much. I'd like to get more, but it would require more filler than I think would be wise. I'm hopeful getting that last 5.5 flat, especially the last 3 feet where the hook is the worst, will result in a major improvement in handing.

Re: Planning Surface

PostPosted: Sun Feb 07, 2016 12:25 pm
by Robert
regarding the planning surface; as stated it relies on many things... However, planning basically comes from the flatter, horizontal surfaces of the bottom. and especially the aftermost portion.
the boat i have has concave areas in the bows were the boat sank into the supports there too. and I think this affects the handling as well.

as for the fairing, I'd be inclined to think that 3/8" would be too deep to fill with putty with out covering it with cloth. I'm guessing that with this deep of a hog, the area needing to be filled will be at least 2' square.most likely more. and that is a lot of area to have a patch of putty.
also, what condition are the ribs in? again i would guess that some might be cracked? too much flex of the wood structure under a large and thick putty patch is going to separate sooner than later.

Re: Planning Surface

PostPosted: Thu Feb 11, 2016 9:35 am
by W Guy
I know this sounds like more work for you, but since the hull was completely flat when it was built, I'd be inclined to bring it back that way and take the guess work out of it. I think you'd be pretty unhappy if you decided to stop when you thought it was "good enough" and then still had problems on the water.....