Resistance Testing-Planing Hull Sailboat

[Doug Lord]

The hull I want to test is almost 18' long and will be tested at different weights. The boat will use a small hydrofoil on the daggerboard and one on the rudder. The point of the testing is to optimize the size of these foils to assure that they actually benefit the design more than they hurt it. The foils are there to improve speed and handling-not to fully fly the boat.( "foil assist") I'm associated with a marine testing laboratory that will help-they'll set up the data collection so that resistance can be accurately measured and referenced exactly to speed and set up to be easily analyzed.
The lab has not done this kind of tow testing before but they have a wide background in testing to various standards of almost every marine component-mostly powerboat components,tanks, bilge pumps, wheels, hydraulics ect.
My proposal is to attach a tow line to a mast stub with the attachment point at the CE of the rig and test between 0 and 20 knots with the boat level(athwartship).
Foils would be tested at different angles of incidence according to a plan that we will develop. The boat will be tested with a "plain" daggerboard and rudder and then with the foil equipped boards.
Some questions:
1) should the towing be done outside the wake of the towboat-will that turbulence affect the results?
2) seems to me that initial testing should be done in flat calm water-no waves?
3) should the tow line from the boat be kept relatively level instead of going at a down angle to the towboat?
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I would appreciate any suggestions or comments particularly if you have testing experience. Thanks!

picture of model of boat to be tested:

[jwboatdesigns]

Ive done some testing on a hull of about this size and proportions, it was a foil stabilised type but my students ( marine design degree, third year) had a ball testing it with all sorts of lift and stabilising foils.

Tow it in undisturbed waters, dead flat water, keep the towline as close to parallel with the waters surface as possible to minimise trim changes, it may help to radio control the rudder so it can be made to track properly.

Hope that helps

John Welsford

Originally Posted by Doug Lord

The hull I want to test is almost 18' long and will be tested at different weights. The boat will use a small hydrofoil on the daggerboard and one on the rudder. The point of the testing is to optimize the size of these foils to assure that they actually benefit the design more than they hurt it. The foils are there to improve speed and handling-not to fully fly the boat.( "foil assist") I'm associated with a marine testing laboratory that will help-they'll set up the data collection so that resistance can be accurately measured and referenced exactly to speed and set up to be easily analyzed.
The lab has not done this kind of tow testing before but they have a wide background in testing to various standards of almost every marine component-mostly powerboat components,tanks, bilge pumps, wheels, hydraulics ect.
My proposal is to attach a tow line to a mast stub with the attachment point at the CE of the rig and test between 0 and 20 knots with the boat level(athwartship).
Foils would be tested at different angles of incidence according to a plan that we will develop. The boat will be tested with a "plain" daggerboard and rudder and then with the foil equipped boards.
Some questions:
1) should the towing be done outside the wake of the towboat-will that turbulence affect the results?
2) seems to me that initial testing should be done in flat calm water-no waves?
3) should the tow line from the boat be kept relatively level instead of going at a down angle to the towboat?
---------
I would appreciate any suggestions or comments particularly if you have testing experience. Thanks!

picture of model of boat to be tested:

[daiquiri]

Doug, are you testing a full-size boat or a scale model?

[Doug Lord]

Originally Posted by jwboatdesigns

Ive done some testing on a hull of about this size and proportions, it was a foil stabilised type but my students ( marine design degree, third year) had a ball testing it with all sorts of lift and stabilising foils.

Tow it in undisturbed waters, dead flat water, keep the towline as close to parallel with the waters surface as possible to minimise trim changes, it may help to radio control the rudder so it can be made to track properly.

Hope that helps

John Welsford

============
Thanks, John! I think I'll ride the thing so I can adjust the foils-if I'm not too scared. It needs the weight anyway. I appreciate your comments very much. Crew weight the same-wing ballast changed....

[Doug Lord]

Originally Posted by daiquiri

Doug, are you testing a full-size boat or a scale model?

==================
Slavi, the full size boat.......

[jehardiman]

For something that size there is always NSWCCD.... anyway...

When high speed models are tested, there is usualy a need for a cricket or two point dyno to constrain the model in yaw as there is no active control to prevent kiteing. On an 18' model yaw may be considerable. A two point dyno will also help in determining the directional stability derivatives.

[Doug Lord]

Originally Posted by jehardiman

For something that size there is always NSWCCD.... anyway...

When high speed models are tested, there is usualy a need for a cricket or two point dyno to constrain the model in yaw as there is no active control to prevent kiteing. On an 18' model yaw may be considerable. A two point dyno will also help in determining the directional stability derivatives.

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As it stands now,I'll be in it steering it -just as I would be under sail.....
PS-what is "NSWCCD" ? Naval Surface Warfare Center CD???

[jehardiman]

Originally Posted by Doug Lord

===========
As it stands now,I'll be in it steering it -just as I would be under sail.....
PS-what is "NSWCCD" ? Naval Surface Warfare Center CD???

As you think: Naval Surface Warfare Center Carderock Division...The David Taylor Model Basin for us old folks. The "slow, deep" tank carriage will do 20 knots, the "high speed" basin will do 50. The models are about the size of your hull.

Two parallel towing tanks are located at the Naval Surface Warfare Center, Carderock Division (NSWCCD), in Carderock, Maryland. One tank is subdivided by a bulkhead to provide two independent basins with separate carriages. The first basin includes a deep section 6.7 m deep, 271 m long, and 15.5 m wide, and a shallow section 3 m deep, 92.4 m long, and 15.5 m wide. The carriage has a maximum speed of 9.3 m/s. The adjoining second basin is 6.7 m deep, 575 m long, and 15.5 m wide, with a pneumatic wave maker at one end and a wave-absorbing beach at the other. The carriage in this basin has a maximum speed of 10.3 m/s. The other towing tank, known as the high-speed basin, is 904 m long with a deep section 4.9 m deep, 514 m long, and 6.4 m wide and a contiguous shallow section 3 m deep, 356 m long, and 6.4 m wide. A pneumatic wave maker is at the deep end and an absorbing beach is at the shallow end. Two carriages are located in the high-speed basin, with maximum speeds of 16.5 m/s and 25.7 m/s.

[Alik]

1. Keep towing line length at least 4 times longer than length of tug boat - this is important to minimize effect of tug's propeller and wake flow.
2. Towing point - it is good to have it at same level as CE of sailing rig;
3. If the model/boat is asymmetrical (if it is stabilized on one side), it will yaw(drift) to one side, so towing rope will not be parralel to tug's CL.

[Doug Lord]

Originally Posted by Alik

1. Keep towing line length at least 4 times longer than length of tug boat - this is important to minimize effect of tug's propeller and wake flow.
2. Towing point - it is good to have it at same level as CE of sailing rig;
3. If the model/boat is asymmetrical (if it is stabilized on one side), it will yaw(drift) to one side, so towing rope will not be parralel to tug's CL.

==========
Thanks, Alik! The boat is symetrical and a full size working prototype.