Whale tail cause for cavitation Yes or No

A

Ancient Mariner

Cadet
Joined
Jul 8, 2003
Messages
14
14'classic wood runabout cavitates during high speed turns. I am running a short shaft 1960 evenrude Lark II 40hp with a Whale tail. <br />Any suggestions?
 
H

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: Whale tail cause for cavitation Yes or No

Whaletails don't usually cause cavitation. <br />After reading your other posting about long and short shaft engines, I'm wondering if you have the shortshaft engine on the longshaft transom.<br /><br />c/6<br /><br />Hooty
 
S

sharkcat

Petty Officer 1st Class
Joined
May 4, 2003
Messages
285
Re: Whale tail cause for cavitation Yes or No

Is the whaletail/cav plate level with the bottom of the boat?Is the prop in good condition?There are lots of variables that will cause cavitation in turns...
 
A

Ancient Mariner

Cadet
Joined
Jul 8, 2003
Messages
14
Re: Whale tail cause for cavitation Yes or No

Currently I don't have the whale tail on but I notice my short shaft engine has the cavition plate 1" below the bottom of the transom. If I put the long shaft on it will be 6" longer but I am conserned about causing too much drag. Also yes my prop is like new. I'm not sure how to tell if my boat is a long or short shaft boat. How far should the cavition plate be below the bottom of the transom?
 
J

Jack Shellac

Lieutenant Commander
Joined
Aug 7, 2002
Messages
1,661
Re: Whale tail cause for cavitation Yes or No

I believe you're experiencing "ventilation" instead of cavitation. This usually shows up on turns when the motor is mounted too high on the transom. The catch is that if your anti-ventilation plate is one inch below the keel, that sounds about right. Is there anything on the bottom of the boat that may be introducing air into the stream of water going to your prop? Are the holes drilled for the whaletail still in the anti-ventilation plate? It's possible that air could be drawn through the holes by the negative pressure side of the prop blades.
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Whale tail cause for cavitation Yes or No

If your motor is trimmed out alot it could cause ventilation in turns also if it is round bottomed<br /> the roll in a turn could cause it too.<br /> Im a little surprised it ventilates that easily with the plate 1" below the bottom.<br /> Definately dont use the long shaft.
 
oldboat1

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,607
Re: Whale tail cause for cavitation Yes or No

I had a similar situation with a '70 Evinrude, and finally resolved it by going to a cupped prop. If your ventilation plate is just below the bottom of the boat, that is proper. I also tried a whale tail, but that didn't solve the problem.<br /><br />I've never looked into prop variations for the 35s and 40s of the fifties and sixties, and I don't know if anything is available. The rounded blades wouldn't seem to lend themselves to cupping, but maybe it would be possible to have a shop do it for you. (I don't think I've seen anything on this subject -- cupped props for period motors, that is.)
 
A

Ancient Mariner

Cadet
Joined
Jul 8, 2003
Messages
14
Re: Whale tail cause for cavitation Yes or No

Still experimenting with different set ups. I had it out the other day without the whale tail and there was no cavitation / ventalation in turns. However, the boat was a real dog on the take off. I am still dialing it in. Thanks to everone for the great ideas.
 
You must log in or register to reply here.
Top