broken cavitation plate

[diggerdan17]

i haven,t had a chance to test drive the boat i just bought ,14 foot starcraft 35 horse johnny .<br />motor runs fine in a pail and have done minor tuneup and whatnot.the cavitation plate is badly damaged on both sides and i was wondering what effect that would have on the performance of the boat.i also have one of those hydro foil fin looking things that is not attached to the broken plate.would installing this hydrofoil fix any problems that a broken cavitation plate would cause?

 

[Texasmark]

Re: broken cavitation plate

I always wondered how the plate could standup to the stress caused by that "whales tail". The purpose (of the contraption) is to put downward pressure on the stern of the boat and thereby assist in getting the bow down, i.e. on plane with small engines and/or high stern loads....like tiller steered type righ or I/O types to name a couple. <br /><br />Not made for high performance functions and actually hinders it if in contact with the water when doing the high performance things......extra drag.<br /><br />The anti-cavitation plate which was designed into your engine is designed to reduce the possibility of the prop sucking air as it turns. Since the atmosphere is right above the turning prop, laws of physics says that it will suck from the weakest point. Since air is lighter than water, it will suck from the top and cavitate (spin up without producing required thrust-forward motion). Putting the plate there increases the distance to the air and reduces the opportunity.<br /><br />I really don't think you will have much of a problem with your setup with it even missing altogether. If you have an older 35, they weren't very big anyway.<br /><br />A prop shop can weld/repair it for you if you wish.<br /><br />I wouldn't reattach the tail to an already damaged plate.<br /><br />My 2c.<br /><br />Mark

 

[JB]

Re: broken cavitation plate

Trivial seeming differences, Mark, but very important, nevertheless.<br /><br />The plate is to prevent ventilation, sucking air as you describe, not cavitation. That is why the correct term for it is the anti-ventilation plate.<br /><br />Cavitation is the creation of vapor on the prop blades by damaged or overtorqued props. Cavitation can be very damaging to the prop surface.<br /><br />The purpose of hydrofoils is to lift, not place downward pressure on, the stern, thus lowering the bow and allowing plane at lower speeds.

 

[diggerdan17]

Re: broken cavitation plate

okay then...i will wait for the ice to come off the lakes and give her a good try.....if i find its venting to much when i turn then i will have a welder fix up the broken plate.<br /><br />once again thanks for the reply.

 

[steelespike]

Re: broken cavitation plate

Just a quick note.You should consider the Fin a last resort modification after a careful proper set up of your boat/motor combo.<br /> To keep it short I have had very good luck with Doelfins on a 15 ft outboard and a 18 ft I/O.No problems with breakage including my moter repeatedly getting stuck in mud and rock at her slip.<br /> For the fin to work as intended it needs to be in the water at speed.Yes it will sap a little top speed but I think you would need a speedo to tell.And I don't think they are good for a high performance boat.