First time boat-builder

[marshmat]

A Canadian single vessel plate has the boat's HIN printed on it. If the boat has no HIN, one is automatically assigned when the plate is printed. Request the plate and you get the HIN too. In Canada at least, the legalities are really quite easy and simple.

[timplett]

That's good to know, thanks.

Tim Plett

[lewisboats]

Thanks for the comments Matt. I actually suggested adding the sponsons to the existing hull, not shortening it with a cutout. I figured a few extra cubic feet of bouyancy back there couldn't hurt. Putting a bit of a hook in the bottom of the sponsons might act a bit like a trim tab, forcing the nose down a bit at speed.

Steve

[timplett]

I made the indent in the transom mostly because it was easier, and I didn't see the difference at the time, I know do. Good thing I saved the original file. What size would be good for the sponsons, and roughly what angle to get the trim tab effect?

[lewisboats]

I was thinking just long enough to extend to where the back of the motor would be. I was also thinking of a 'hook', but on second consideration, it wouldn't work with a vee bottom. You would be better off with some external tabs to help deflect the flow downward a bit.

Steve

[timplett]

So are you saying to completely scrap the sponson idea and use tabs instead of to use a combination of the two?

[marshmat]

I agree with Steve on the hook... hook is great at slow planing speeds but for a zippy sportster you'd be better off with a plain V, a hook would force the bow too low at speed and make control difficult.

[lewisboats]

I think your best bet would be adjustable trim tabs. These would allow you to add tab to work the nose at slower speeds and reduce tab as speeds increase and you get more hydro-dynamic lift on the aft end of the boat. You will not get rid of the nose lift, as this is inherent in the short length of the boat, but you might attenuate it a bit as you progress from displacement speeds thru slow planning speed to high planning speed.

[timplett]

Tweaked the design, lost the sharp chines, narrowed the beam 6", moved the cockpit (or whatever you want to call it) forward 1.5' to offset the trim some. Thoughts, comments, criticisms please.

[marshmat]

Some good progress, Tim.
Pull up the curvature graph for the chine (select the chine, then Curve->new, f10 to increase scale). At the 3rd point from the stern, the chine curvature changes direction. I'd pay close attention to making the chine and keel as smooth and fair as you can; abrupt changes in curvature are hard to build and make control at speed difficult.

[timplett]

I smoothed all the curves as you suggested marshmat. The keel was the hardest, and still isn't perfect by any standards but I think it is much better. I started just numbering the files because I keep saving so many different versions as I go to make sure I can easily go back to before I made the changes. .: This is file 4.

Thanks for the help.

[SamSam]

There is a bunch of older plans at this site. Maybe looking them over will give you some ideas on what might work for you. Sam
http://www.svensons.com/boat/

[lewisboats]

Looking much better. Just a little point here...I would smooth the bow/chine intersection. Simply removing the checkmark in corner box of the point properties does a nice job of rounding over. Oh, and there are .bak files to rename also if something goes squirrely.

Steve

[timplett]

I unchechecked the corner checkbox but it keeps rechecking itself.

[antonfourie]

Tim, something else to be aware of is that outboard manufacturers tend to have two HP models that weigh the same i.e Yamaha 9hp & 15 hp is the same weight so check that you are getting the higher HP for the weight, you may even be able to get a lighter outboard by dropping 5hp