DE23 displacement speed

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pompom
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DE23 displacement speed

Post by pompom »

Hi Jacques,
How HP to displacement speed for the DE23 (sail just in canals in Europe).
Thank you,
POMPOM

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Re: DE23 displacement speed

Post by jacquesmm »

No wind? 10 HP (7.5 Kw) will move it but I would go for a 25 HP (around 20 Kw) to have safety margin.
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pompom
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Re: DE23 displacement speed

Post by pompom »

Is like the GT 23, O.K. and thank you,
POMPOM

AlScal
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Re: DE23 displacement speed

Post by AlScal »

(a rule of thumb) 2 to 4 hp per ton will allow most boats to achieve hull speed

Matt Gent
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Re: DE23 displacement speed

Post by Matt Gent »

Agree on a 25hp as a single engine. Even a 15 would pretty reliably get to hull speed. You'll want the biggest prop diameter you can get (high thrust, or command thrust version), and check on the availability of very low prop pitches to get into the right RPM range. Most of those engines are set up for planing boats.

Some related discussion is here from when I was setting up a kicker for DE25
viewtopic.php?f=2&t=64080&p=446257&hilit=df6#p446257

It would go about 5mph (no tide, no wind) with the 6hp and the standard prop. I now have a smaller pitch prop, but haven't tried it on that boat yet. Also haven't tried it in larger seas. You would definitely want at least a 20" shaft. Maybe one of the models that is set up for sailboats.

TomW1
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Re: DE23 displacement speed

Post by TomW1 »

PomPom I ran your specs through my calculators using the numbers from the study plans a yamaha 25 and other figures I have. The max speed should you ever need it is 19 mph with the 25. The hull speed is 6,9 mph. The prop recommended was a ss 9,5d x 8p

You would get excellent gas mileage running @2500 - 3500 rpms, you will just have to try each and see which is best. Watch your tach,

Good luck on your build, the DE23 is a lady.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Matt Gent
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Re: DE23 displacement speed

Post by Matt Gent »

Looking at the performance curves from my boat, 25hp is getting nowhere near 19mph on a DE23. Based on fuel consumption I need a little over 60hp to get over the hump to the high-teens. Even assuming a 23 could be a couple hundred pounds less, and the motor 150-200lb less (and operating more efficiently at low power levels), and carrying less stuff, I think that's a stretch. 12-13mph up against the hump, with any reasonable loading, is more likely.

A 23' cruising boat optimized around the 25hp and mid-teens speed would have the LCB another foot or more forward, have some rocker, and tuck in the transom instead of the parallel buttocks on the DE. That would make a sweet canal boat.

Edit to add: something like Ross Lillistone’s Three Brothers could do it. I actually bought plans for this and planned to build it before I found the DE. It is quite a bit less boat than a DE, and the assumes displacement for performance numbers in this link are about 1000lb less than I’d think a DE23 would cruise at
https://www.duckworks.com/product-p/ros ... ers-id.htm

TomW1
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Re: DE23 displacement speed

Post by TomW1 »

Matt there is no hump in the DE23. She has a monohedron hull that does not form a hump.

"The hull type is similar to what is now frequently called a picnic boat; a seaworthy planing boat but the topsides are more in the
Down East cruising boat style. We kept the deep forefoot of the modern fast lobster boat hull but the underbody is a
true monohedron. This means that the transition to planing speeds will be smooth without any excessive change of
trim and without the wasteful suction of warped bottoms running at an S/L higher than 2.
(S/L ratio is speed in knots divided by square root of WL in feet. Displacement boats are the ones with an S/L<1.3,
planing boats have S/L>2)
The Down East 23 will perform well at displacement speeds in bad weather and run efficiently at moderate planing
speeds with relatively small engines."

I should not have said 19 but have better said upper teens 16-19, depending on conditions and loading. This is a max speed under ideal conditions. Normal operations would be lower.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Matt Gent
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Re: DE23 displacement speed

Post by Matt Gent »

Those study plan words are nice, but having put a couple thousand miles on my DE25 it has a noticeable hump. I've measured it to peak around 4 degrees, through the mid-teens. To the upper teens it drops back down to about 1deg. Yellow curve below (no y-scale). That's not bad, but it's not nothing. I think it has more to do with Cg and Cb location; my other monohedron speed boat will pitch way up over 10deg planing off, but it has a huge aft bias for top speed.

Image

The Crouch #s start to fall apart as speeds come down into the transition range. I've plotted the crouch curve up for my boat, and vs. effective hp (scaling fuel consumption by an estimate of BSFC). The crouch under-predicts actual power required by about 30% in the transition zone. It's really accurate above 18-20mph, or S/L of 3 or so.

I'm sure a DE23 with a small engine and no bracket will be better than mine in terms of trim. But I still think it won't plane, and will stick up against the hump at WOT with only 25hp.

Another reference: B&B OB20 goes 20mph on 25hp, weighing ~1000lb less than a much larger DE23 ready to cruise. https://bandbyachtdesigns.com/ob-20

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Re: DE23 displacement speed

Post by TomW1 »

Matt, that is fine for the De25, but remember as you stretch a boat, with out a corresponding width increase it becomes less efficient, your 25 is 9% longer but only 2% at the beam and I don't know how much at the water line if any, losing the advantage of the hull design of the DE23 yet maintaining part of it and a very efficient boat. You are basically sitting lower in the water. I am so glad you are getting so much use out of yours.

Keep on with your letting us know of your adventures. Your boat is a beauty and so glad you are getting such great use of her.

Regards, Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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