Flooded Hull Boat ???

This is a small 6/16 custom-built boat I have been working on for some time. I have enclosed the tunnel and left the back of the tunnel open so that when at anchor or low speeds the tunnel fills with water to give "free ballast". The boat is exceptionally stable. My question is where to mount the engine with respect to the bottom of the tunnel. At, present I have a lot of spray. This is a one of a kind type boat so I am on my own with the design.

Here is a picture of the tunnel which is enclosed about 2/3 of the hull length (covers the tunnel). You can click on the below pic if you want to look at more pictures. It has been a challenge.

I am open for ideas. I have posted this question several places.
http://i188.photobucket.com/albums/z...psae566fdf.jpg

Did you ask on ScreamandFly.com? A lot of those guys are into racing tunnel boats and should have some good dope for you.

What kind of spray? From the LU or the prop or somewhere else?

Kind of hard to judge angles, but it looks to me like your prop shaft is going to be fairly shallow when you trim down. How fast does the boat go, and at what speed do you get the spray?

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Originally Posted by CatFan

What kind of spray? From the LU or the prop or somewhere else?

Kind of hard to judge angles, but it looks to me like your prop shaft is going to be fairly shallow when you trim down. How fast does the boat go, and at what speed do you get the spray?

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Looks like a plow breaking ground at high speed. I can't see good when driving. Boat goes about 25mph. The anti-cavitation plate is about 2 inches below the bottom of the boat.

Raise your motor up.....put the cav plate even with the bottom of the boat is what I am thinking......worth a try anyway. I think it should be even with your trim tabs on the boat.

Raise the plate up even and try it Cane, the plate may be causing the spray.

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Originally Posted by Cane Pole

Looks like a plow breaking ground at high speed. I can't see good when driving. Boat goes about 25mph. The anti-cavitation plate is about 2 inches below the bottom of the boat.

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You want that cav plate closer to the top of the water. You may have to invest in a manual jackplate to dial in the position.

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Originally Posted by "G"

Raise your motor up.....put the cav plate even with the bottom of the boat is what I am thinking......worth a try anyway. I think it should be even with your trim tabs on the boat.

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Think we were typing at the same time, seems to be an echo in here!@!!!:Rofl

Tunnel boats were designed for operating in skinny waters. Normally a jet drive would be installed on a tunnel boat and the motor, regardless of drive, would be mounted higher than normal to take advantage of the tunnel. But since Tom apparently blocked off the front of the tunnel and it is drastically affecting water flow when moving. I've never heard of anyone doing that mod to a tunnel but then there are a lot of things I have never heard of. Or just plain forgot. Interesting tho.

I believe Swift boat makes one. Can't remember. They are out there but not in numbers.

Google Image Result for http://www.boatdesign.net/forums/attachments/boat-design/11397d1170460016-flooding-hull-fjordling_17_006.jpg

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Originally Posted by Barnacle Bill

Did you ask on ScreamandFly.com? A lot of those guys are into racing tunnel boats and should have some good dope for you.

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Treied. I can't log on for some reason.

Here is an animated video of the flooding hull, but much more extreme than my dink.

Flooding Chamber; surtees secret weapon; fishing boats nz

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Originally Posted by Cane Pole

Here is an animated video of the flooding hull, but much more extreme than my dink.

Flooding Chamber; surtees secret weapon; fishing boats nz

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That is pretty neat but would be a long drive home if you bought one.

Looks like a plow breaking ground at high speed. I can't see good when driving. Tom, I assume you are getting spray up forward if it is affecting your ability to see, not off the aft end? Do a search on hull spray rails, and it might be something for you to consider. Here's a supplier of after market spray rails. Home A little pricey, but a single 9 footer cut in half might work for you.

Maybe someone video taping you while running might help to see what's causing the spray.

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Originally Posted by Shellback

Looks like a plow breaking ground at high speed. I can't see good when driving. Tom, I assume you are getting spray up forward if it is affecting your ability to see, not off the aft end? Do a search on hull spray rails, and it might be something for you to consider. Here's a supplier of after market spray rails. Home A little pricey, but a single 9 footer cut in half might work for you.

Maybe someone video taping you while running might help to see what's causing the spray.

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Spray is aft. Boat runs with an slight nose up attitude. No spray up front. Hex shape of the pontoon deflects spray away from the cockpit. Dry ride, even in choppy water.

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Originally Posted by Cane Pole

Treied. I can't log on for some reason.

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No problem here.

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Originally Posted by Cane Pole

Spray is aft. Boat runs with an slight nose up attitude. No spray up front. Hex shape of the pontoon deflects spray away from the cockpit. Dry ride, even in choppy water.

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Okay, the can't see where you were going lead me to believe the spray was off the bow.

Have you tried trimming your motor? Or do you have trim? If not try moveing your motor one notch to under trim to bring the bow down. I really don't understand what you are saying here.

Is a pressure wave forming forward of the motor?

The spray is aft. It is spraying up on the gas tank and the steering actuator in the aft baskets. I put some solid aluminum pieces on the bottom of the trays to keep the water off the actuator. It is a heavy spray. Must be coming from the engine. I can't see. I will hook up my camera the next time out.

Moving the engine up and down holes requires me to remount the steering actuator. A big job. Yes, I have PTT.