boat spped - the formula

[Rob Ripley]

I quote John sometime ago ...

...' The Seagulls were never designed to exceed the displacement speed of the boats, so for a 2.5 metre boat, measures at the Waterline you would only need 2.5 hp to get it to it's top speed of 2.5 knots. This formula works well enough for all displacement boats up to 30ft.'...

Has anyone tested the formula with the same motor on a clinker/displacement boat of 8', 10', 12' etc ?

If the formula uses metric measurements, with the result be in Klms ?

I'm inserting 6' in my 8' dinghy, so I'll be interested in the increase in speed ----- IF ANY !!!

[Horsley-Anarak]

I'm inserting 6' in my 8' dinghy, so I'll be interested in the increase in speed ----- IF ANY !!!

My Father added 6' to the middle of his 18' steam launch. At 24' it is much quicker than it was.

For a non planing hull there is a direct relationship between waterline length an speed.

Your boat will go faster, I would try and keep the weight down if possible.

I found the place to cut my fathers boat with a pair of parallel string lines, he would not let me cut it though.

I would think that you will need to be careful about the shape, so that it does not get to wide in the middle. Or that you don't end up with a flat spot in the middle.

Good luck

H-A

[Rex NZ]

Rob

To get more displacement speed from your seagull the hull wants to be;

* long &
* narrow with
* flat bottom
* little or no vee with
* no rocker curve
* lightweight

A hull called the 'Bermudan Flea' represents these design features fairly well. I seem to remember some plans available elsewhere in this forum

Rex

[Rob Ripley]

Thanks for that H-A,

... found the place to cut my fathers boat with a pair of parallel string lines, he would not let me cut it though...

I just found the spot at the greatest beam and ran a line around the hull.
[attachment=0]DSCF7363.JPG[/attachment]

... I would think that you will need to be careful about the shape, so that it does not get to wide in the middle. Or that you don't end up with a flat spot in the middle....

I was careful ... and did end up with a flat spot.

Rob

[Horsley-Anarak]

I was careful ... and did end up with a flat spot.

Rob

Great picture Rob.

Got any more pictures of it stretched ?

H-A

[Rob Ripley]

... Got any more pictures of it stretched ? ...

Yes. hundreds !!!

[attachment=0]PA162200a.jpg[/attachment]

I constructed a frame to keep the halves in line and provide a stable platform.

[skyetoyman]

will you be be extending the trailer the same way.
The only way I would add 6 feet to my boat would be from 3 anglers

[Charles uk]

That might work well for me, I break down so often (I'm told) 30 tows in credit could save my bacon!

[Rob Ripley]

.... will you be be extending the trailer the same way.

Don't need to, looks like it'll have about a foot (or so) overhang, I'll just make up a lights and numberplate board and fasten it to the transom when it's on the road. As it happens that trailer has an extended main bar, to suit the different boats I have.

[attachment=0]RIMG1710.JPG[/attachment]

[Rob Ripley]

And before the subject drifts downstream .... 'boat speed - the formula"

Has anyone tested the formula with the same motor on a clinker/displacement boat of 8', 10', 12' etc ?

If the formula uses metric measurements, with the result be in Klms ?

[GULLABLE TEXAN]

Would anyone (Horsely-Anarak perhaps) have any comment on the Swift Canoe (SC-16), with plans by bateau.com the designers. It seems to mimic a numbers of the designs used by seasoned Gull racers around the globe.

[Horsley-Anarak]

Would anyone (Horsely-Anarak perhaps) have any comment on the Swift Canoe (SC-16), .

http://www.bateau.com/boats/SC16/

Yes it is very much like my grey boat, as are some of these

http://www.selway-fisher.com/Mcanoe.htm

Long thin and light, low displacement quite quick.

The SC 16 should go well with a Seagull on the back.

H-A

[GULLABLE TEXAN]

Best news so far H-A! When the path follows the track of the scouts, one may get to the right place. Thank you for the additional link.Now I must look to the building of one of these designs, I will have to compare lists of materiels, simplicity of build, required tooling, and costs to prepare for a choice of plans. Any advice or thought on a sturdy, simple to build design will be carefully considered. Not having done a boat before, we want to build at least one here with the wife's 5th grade science class to learn the pratfalls. We want to lure them away from video smart phones and out into the shop. If we can learn and teach at the same time, we stand a better chance of being able to build the boat in a week in Bermuda. We want to then donate the boat to some youth group on the island when we leave. Comments on possibilities of success or grounds for being certified insane welcomed...

[Horsley-Anarak]

My wife is also a teacher and I am often involved in making their days at school exciting.

As you are in the states it is well worth studying http://www.duckworksmagazine.com/index.cfm.

There are loads of plans on there. Materials suppliers, techniques.

Also google "stitch and glue construction", there is masses of information for first time builders.

It is worth building a small simple "free plans boat" just to see if you like boatbuilding.

Substitute epoxy with polyester, and use cheaper external plywood rather than marine ply. Build it in a weekend and stick it on the water.

If it only last for 5 to 10 years with lesser quality materials so be it. I think some people are put off by the initial expense of the plans, marine ply and epoxy.

For a school project, boat building using stitch and glue is a great idea. Very few tools are needed, and it all happens very quickly if you choose a design with only a few components.

The only tools that are needed are a few hand tools, jigsaw, drill and a small sander.

Get building.

H-A

[GULLABLE TEXAN]

Thank you H-A. You have nailed our situation as being poverty riddled teacher class boaters. I will follow up on the links and homework. My wife rows a 14ft aluminum skiff a mile each way to the other side of a 68 mile long lake to her old wagon and then commutes another 25 to teach. Gets a little tiring in 30 knot winds blowing light sleet, but she's a sturdy girl... Her class loves her adventures. You might follow www.solotheamericas.org to follow,live, our son's trek around the continents alone, non-stop in a 27ft Alden-Vega sloop. He made it through the NW Passage and is now in the Pacific headed for the Horn.