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Dishing out the chine

Posted by Sandy 
Dishing out the chine
November 23, 2015 09:29PM
Here I am dishing out the chine edge on an 18' foot side panel, so it is no longer a straight line, so a widely-flared boat doesn't end up with too much rocker. Warping the ends of the side panels slightly, by having more side flare in the middle and less side flare out towards the ends also contributes--some--to reducing rocker. You can also reduce rocker at the upstream end of the boat by widening the transom a little. If you want a nimble, easy-to-spin and turn boat you need just enough rocker to make that happen. But not too much. Dishing the chine a lot in the middle and very little out towards the ends of the boat, combined with a bottom width profile that is almost but not quite parallel in middle 4' of the hull, produces a boat that is almost but not quite dead flat in the middle. With all the rocker pushed further out to the ends of the boat. I want a bottom width profile that is symmetrical either side of the middle. But a side-view profile that has more rocker at the upstream end and less at the downstream end..........just enough upstream end rocker to keep the transom out of the current at all times. Less rocker up front helps the boat climb up on the big waves instead of punching into them.

This plywood will be used to make a temporary boat shaped plywood form or plug. It won't be part of the actual boat. I used 6" fiberglass tape over both sides of both scarfs in these panels, so I can bend them repeatedly--during the design process--without worrying about the scarf joints breaking.

I cut two side panel pieces from a 4x18' foot panel. After dishing out the chine edge by almost 3-1`/2" inches the resulting panel is only about 21" inches in the middle of the boat, below the oarlocks. That's not high enough, for most people anyway, for big white water boat. But the actual side panels will be 3/4" inch Plascore held tight to the plywood plug, prior to fiberglassing. I'll make those panels wider, so they overhang the plywood plug by 4" or 5" inches. I might have to fiddle with the plug a bit to make that work. I only had enough plywood to make one 4' x 18' foot panel. So I'm making it work somehow. I do have lots of Plascore.

Re: Dishing out the chine
November 24, 2015 03:59AM
For what it's worth I need to think about this before cutting. The photo above shows a chine dished out symmetrically, with the high point of the dish dead center.

But I want more rocker at the upstream end and less up front. So I'll rework that curve a few times before I'm happy with it. I think I'll take a few days off at this point, in addition to turkey day, and play with a 1/6th scale model where 2" inches equals one foot. My last model at 1/12th scale and roughly 18" inches long (one inch to one foot) was too small to judge well. a 36" inch model, probably made from a large semi-rigid hard plastic "For Sale" sign, will be easier to judge from.
Re: Dishing out the chine
November 24, 2015 04:16PM
Yeah that's not my way of doing it. I prefer to work with one long dish, where the high point of a long continuous curve is not necessarily at dead center.

Doing it my way is a bit like building a boat with a straight line chine, which starts out with too much rocker. And then the boat builder (conceptually) uses a high energy laser to chop off some of the bottom, so the boat ends up with less rocker in the middle and more at the ends, but not symmetrically so. Nearly flat in the middle with 6" to 8" inches of rocker rising fairly sharply up front. With 10" to 14" inches of rocker (for a 17' foot boat, made with 18' foot side panels) at the upstream end, below the transom.

I want one long graceful dish. I have my reasons.
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