The weather says launch

[Wayne Grabow]

Last weekend we had snow, but Spring has finally come. Been making slow but steady progress on a launch of my own design for two years. Having only modest powerboat experience, and none at this altitude, the design has been a learning process. My concept was to build a trailerable, comfortable, moderate-speed launch capable of taking at least four people on day trips in the beautiful mountain lakes with enough speed to get home quickly when needed. The sun here is very intense, usually with little cloud cover, so a bimini top was included.

The hull shape is a semi-planing, variable deadrise design with 2.5 degrees of rocker in the run. I had originally planned for 25-30 hp, but was advised during building that I needed more power, so I chose an ETEC 50 hp. With three people onboard and the bimini top rigged, we achieved 25 mph. We were at 4700' altitude (high lakes are still iced in) so the propellor didn't have quite enough pitch, and the engine would over-rev slightly if allowed.

[IMP-ish]

Looks great Wayne!!!

I haven't ever owned a boat of this style but looking at your pictures I can sure see myself on that lake ... admiring your boat on a day like this!

[Dean Smith]

Well Done!!

[cthippo]

It looks like she's levitating in that first picture. Beautiful boat!

[Wayne Grabow]

The lake we were on is considered pretty ugly compared to the mountain lakes which are at 9000'+. We still could see snow-capped peaks in the distance and visited some cormorant and heron nesting sites.

[F3M4]

That is a good looking boat.

[ancient kayaker]

Originally Posted by cthippo

It looks like she's levitating in that first picture. Beautiful boat!

That's 'cos the water is so clear, which is probably because it's cold. Don't fall in !!! - yet.

[Wayne Grabow]

Thank you for the kind comments. I really enjoyed designing and building the boat and plan to do it all over again after I test this one out more. I am happy with the result but still can see many places to improve on.

Lake Pueblo is fed by melting snow through the Arkansas River and is refreshingly cold at this time of year.

[claydog]

Originally Posted by Wayne Grabow

Thank you for the kind comments. I really enjoyed designing and building the boat and plan to do it all over again after I test this one out more. I am happy with the result but still can see many places to improve on.

Lake Pueblo is fed by melting snow through the Arkansas River and is refreshingly cold at this time of year.

LOL on the bold. Nice job on your boat.

[Wayne Grabow]

After switching to a higher pitch prop, we are up to 30 mph with this "semiplaning" hull. Although the hull has some rocker to the run and my focus was on moderate speeds, I did hope that it would plane efficiently, and that appears to be working out.

[nukisen]

Looks like a very good design job Wayne. She looks fine and seems to function well in water. What more can a man desire?
Congratulations.

[hoytedow]

Very well done!

[Wayne Grabow]

After switching props again the boat is up to 33 mph, and that was on Blue Mesa Res. at 7000' altitude. I think I can get at least 35 mph at lower altitude. This has been such a fun project that I have already built ten of the frames for a newer design. One of my coworkers is interested in buying this boat when the new boat is completed. That should be about summer of 2013.

[Easy Rider]

Wayne,
I have a very similar boat and almost identical engine. I do'nt know how fast it goes but it's plenty fast......I'm guessing at least in the high twenties. It's performance is excellent no mater how much weight I put in it. I do have a slightly lower pitch prop than what came w the engine. Of course the run of the bottom aft is straight but I almost never go over 20 mph so a slightly less than full planing hull would be better for me but such a boat is nowhere to be found. That brings me to the reason of my post. I've always seen rocker expressed in inches. I'm trying to get an idea of how much rocker you've got in your boat. It could'nt be much (me thinks) since you're running over 30 mph. Can you tell me how many inches of rocker 2.5 degrees is?

Easy Rider

[Wayne Grabow]

First, Merry Christmas! Then on to your question: At rest afloat, the bottom of the keel at the middle of the boat is about 3" deeper than at the stern. But that is the simple answer since this is a variable deadrise hull. The keel is straight (but not level) from the middle to the stern of the 18.5' hull. The chine slopes downward from the bow until a point about 7' from the stern where it levels and then curves upward very gradually. It is only parallel to the keel for the last 28" at the stern.

Of course, at speed, the bow rises 10-12" to put the entire bottom at a positive angle of attack. The transition to planing is gradual, best noted by watching the tachometer; increased rpms cause little increase in speed until planing begins.

That said, the next hull will be constant deadrise for about half its length. I find that I spend the great majority of time at planing speed (more than 10-12 mph). Constant deadrise will also mean slightly increased deadrise to handle waves better. The constant deadrise will also be slightly easier to build.