Theory of edge strakes

[Jeff Torgalski]

Hello everyone,

How's the weather treating all of you?

I was wondering if anybody has knowledge they might want to share about edge strakes on Tunnel Hulls. What do they achieve, and does anybody know of any places where we could find more information on them? If you know some things, please chime in.

Thanks,

Jeff Torgalski

 

[Grimracer]

Jeff

Strakes provide lift to the boat. I would ask Timboat about them. Timster are you here?

Bottom line is lift.

O yea we still have ice on the water... Another week or so and it will be gone.

Grim

 

[GTR]

Hi Guy's,

Edge strakes definately add lift to the hull, partially as a result of reducing water drag up high on the riding surface of the sponsons and non-trip area. Clean discharge of water from riding surfaces reduces parasitic drag.

Strange observation though is that my mates 7.5WOF hull has them and when he turns he often executes a beautiful barrel roll. It looks very much like the strake on the outside is tripping up the sponson rather than allowing it to slide. JD might be in a position to comment on this with a trim suggestion to eliminate it.

Jimboat would look forward to your expertise on the benfits/negatives for strakes. Do vents in the riding surfaces (as opposed to steps) assist with providing lift and drag reduction also?

thanks for any insights

GT

 

[Jerry Dunlap]

I have just finished a new JD WOF 30(plans available in about two weeks) and have outside edge strakes on both sponsons. I've run the boat with a stock K&B 3.5ss and I honestly believe it's going as fast as my Villian S1 and the fellow who was with me when I ran the boat agreed it was definitely fast. The boat is somwhat like a Villain - hey, I ain't proud, if something works I'll copy it!!!

I created the strakes by extending the tunnel side sheeting 3/32" below the outside edge of the sponson and then creating the strake by filling in the extended plywood.

The boat corners great without any stumble blocks and really rides clean because the strakes are sheering the water. I'm going to attempt to attach a photo of the back of the boat.

Jerry D.

 

[Jerry Dunlap]

Well, that worked. If you look closely, you can see how the sheeting extends past the sponson bottom and then is back filled to create the strake. I'll attach another photo of the hull with the balsawood canopy cowling on it.

Jerry D.

 

[Jerry Dunlap]

I'm on a roll now. Here's a photo of the bottom of the boat showing the strakes.

Jerry D.

 

[Jerry Dunlap]

Here's an interesting note - well, I think it's sorta interesting. The width of the sponsons doing the stakes this way is actually less than the sponson width of the Villain S1. I have been doing strakes this way for the past two boats and I think it helps keep the boat from digging in the corners. This might explain the ability to corner without digging in and employing stumble blocks.

J.D.

 

[waterbug]

LOOKING GOOD JERRY !!!

I can't wait to get started on the hull !!! That picture is like rubbing salt in my wounds !!! I'm sitting here on 5 cowl 's ready to go !!! Sorry Grim, thats a

" DUNLAP ORGINAL KNOW "

DUNLAP WOF 28/30

;D

JERRY What kind of cowl is that ??

O' WELL I guess I'll have extra cowls !! TopFuel !! You need more cowls ? he he he !!

 

[Eric Perez]

How can I get plans for the JD 28/30WOF hull? :'(

As a fellow boat - I mean submarine designer I like to see how others are able to fix common handling problems.

 

[waterbug]

Eric

From DA " MAN himself !!!

Until the article gets published in Boat Modeler magazine .

Then you must get them from the magazine.

 

[GTR]

Hi JD, Guy's,

I'm really hanging out for the big new WOF plan. JD I've noticed that you've gone back to the crowned sponson design - more like your earlier designs WOF, sprints etc.

Do you think they help handling in cross-winds. eg balance lift on top and bottom of sponson when side on to the wind.

Very aero looking cowl - not much side profile there to get knocked about by the wind.

Another fantastic JD design about to get splashed. JD have you tried different transom inset depths for the new WOF depending on the OB set-up eg OS, Lawless, K&B leg.

Thanks for your wealth of knowledge and experience.

cheers

GT 8)

 

[Jerry Dunlap]

I went to the crowned sponson top because the boat might become a plug for a fiberglass hull. But, if that happens at all it would be at least 12 months or more in the future. Also, I wanted a little difference in appearance between the JD WOF 30 and a larger Villain that Mike Z. is considering. Personally, I don't think there's any performance gains between a flat sponson top and a crowned top deck. But, I'm a retired school teacher, with no formal training in aeronautics. I actually have another WOF 30 with a flat deck. I think I like the look of the crowned deck.

When I'm going to run a LawLess Outdrive, I like to insert the transom about 1 1/4". For a K&B lower unit the insert is about 7/8".

Jerry D.

 

[Jeff Torgalski]

Wow, I sure am glad I asked. Now I want to make one of those WOF 28/30's.

 

[Grimracer]

Jerry

Did you read what jeff said....he wants to build again....YEA

To me it matters little what you build (A villiain is cool) but as long as you build, and not just put parts on glass.

Welcome to modeling jeff.. ;D

Grim

 

[waterbug]

Jeff

I feel the same way !!! I bought a set of D27 plans and know I think I'm going to hold off !!!!!

LOVE AT FIRST SITE !!!!

I have cowls for two boats and one extra !!! I might , might !! build "1" D27 :'( :-

 

[topfuel443]

Hey Waterbug, I could possibly get an extra cowl from you if you still have an extra, Remeber im running three tunnels next year, so I need one more cowl for my 7.5 project. ;D

James

 

[waterbug]

I might be able to help you out !! but don't know right know ?? Jerry has thrown me a " HELL OF A CURVE BALL " know !!! :'(

Do you like what you see ?? Looks close to what you are building now !! Are you going to get some plans from JD on the 7.5 ??

;D

 

[topfuel443]

Depending on how this first attempt at scratch building a tunnel hull goes, i will probably design my own setup, of course using the info given by guys like Jerry and Grim and Gene. I think its more fun that way.

~ James

 

[Kris Flynn]

Hey Mr Tunnel,

Do you have an estimated cost on the magnificent (spelling) plans we have been waiting for?

How will you be selling them? in a CAD format, or on paper? Both?

Oh yeah, will it be possible to make the boat using the frame method (like the Villain), rather than WOF?

I want to get a Villain, but if i cant work something out, then i might have to go with this boat

Thanks

Kris

 

[Jerry Dunlap]

Kris,

Check the post concerning plans for the JD WOF 28/30.

I suppose you could use the drawings to make frames for the boat. The reason I use WOF construction is to eliminate making frames or than the formers for the foam parts. Also, I've have much less problem with plans for WOF designs than I have had with the plans for the Dunlap 27.

WOFman Jerry