Hydroplane hull design: catamaran or "standard"?

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SoloTSi97
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Hydroplane hull design: catamaran or "standard"?

Post by SoloTSi97 » Wed Sep 26, 2007 12:14 pm

Our regatta is coming up and after doing well last year with a catamaran, my son and I are looking to up our game this year. Last year, there were two catamarans (ours and another boy's). My son, a Tiger last year, came in second behind the other catamaran. I'm guessing that there will be a large number of catamarans this year, so I'm looking at the hydroplane. We have some rules that limit how creative we can get, but catamarans are allowed.

Here's my question. Most of what I've seen talks about the catamaran and the hydroplane as an either/or. Has anyone tried a catamaran-style boat with the hulls cut with a hydroplane profile? I'm curious as to whether this would gain the speed of the hydroplane hull design, but keep the stability and straight tracking of the catamaran.

Thanks in advance for any advice. I've already jotted down a lot of good notes to apply in designing and building our boat. I've got a couple of extra kits, so I may build a hydroplane and a catamaran/hydroplane to test if no one has any input.



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Re: Hydroplane hull design: catamaran or "standard"

Post by SoloTSi97 » Fri Oct 12, 2007 8:59 pm

Well, since I didn't get any input, I built one of each.

I built a "standard" hydroplane BSA-hulled boat and a catamaran with hydroplane-shaped hulls.

The catamaran was by far the faster boat, though these were quickly-built test boats. I suspect that building a hydroplane from the BSA hull is tricky business when it comes to make it go straight (which was the biggest problem with mine).

The catamaran tracked straight (as catamarans typically do). Compared to last year's boat, which was strictly a catamaran, the hydro-cat was measurably faster.

In repeated testing, my son could manage just under 7 seconds over a 10 foot gutter. He managed to get this year's hydro-cat down close to 5 second flat. The hull design wasn't the only design change this year, though, so that is likely not an accurate indicator of how big a difference the hull made. In addition to the hull shape change, we moved more weight aft and mounted the sail farther aft as compared to last year. I also added "bumpers" of sorts, but this was added after I did my timings. The bumpers definitely helped the boat keep from sticking up to the side of the gutter and probably shaved a little more time off on average.

My son and I were very happy with the boat's performance. Last year, he finished first in his Tiger Cub den and second overall to another very capable catamaran. This year, he won his wolf den and placed first overall as well. There was a much larger number of catamarans this year, including a couple that finished within 2-3 boat lengths of ours. But, that was about as slim as the margin of victory got.

Now to start thinking about the derby in a few months ...

Last year's boat:
Image

This year's boat:
Image



Teeeman
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Re: Hydroplane hull design: catamaran or "standard"

Post by Teeeman » Tue Nov 27, 2007 4:05 pm

What was the weight of each boat in grams?

Can you build legally from Styrofoam?

-Terry


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SoloTSi97
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Re: Hydroplane hull design: catamaran or "standard"

Post by SoloTSi97 » Wed Nov 28, 2007 9:10 am

Teeeman wrote:What was the weight of each boat in grams?

Can you build legally from Styrofoam?

-Terry
I don't know, and I understand that weight could likely have been a factor in the speed difference (and, frankly, I didn't care what the reason was ... I just knew I had to build a boat in a relatively short period of time :D ). As they were only test boats, I don't have them any longer to weigh and compare.

Our rules required the use of the balsa block in the kit, so styrofoam was not an option. Our rules further required the use of a mast, and that the sail be mounted to the mast. The sail also could not be altered in size or shape. We were not required to use the rudder or keel.

-Bob



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Re: Hydroplane hull design: catamaran or "standard"

Post by Teeeman » Wed Nov 28, 2007 9:37 am

Wonder just how much you can hollow out the Balsa… or better, how specific your rules are on using it…

i.e. our PWD rules say “must be made of pine” but allow a lot of other freedoms such as plastic drivers, etc. and don’t specify how much has to be pine… so I added “the axles must insert into pine” to our rules… but even that rule would allow us to make 2 sticks of pine to stick the axles into and build the rest of the car from anything else we choose!

Maybe you have similar flexibility in your rules to exploit?

:)

-T


"I dunno..." - Uncle Eddie, Christmas Vacation

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