Where should my cav plate sit in the water on a Volvo Penta 280?

[arfaname]

Gday all,<br /><br />I have a 21 fot glass boat with a Volvo Penta 280 sterndrive. When underway and on the plane the cavatation plate is sitting at leat 2 inches under the water line. Is this correct and if not how do I correct this problem? Will a set of trim tabs correct this? It has a Permatrim plate on it. <br /><br />Would this effect the top speed of the boat. I feel it should be going faster for what it is. <br /><br />21 ft, 302W, top speed 45km/h. <br /><br /><br />Regards<br /><br />Sean

 

[U_U]

Re: Where should my cav plate sit in the water on a Volvo Penta 280?

As a rule of thumb the plate should level with the keel line.<br /><br />The keel (or hull lowest part) is somewhat lower than the waterline, depending on the hull design (deadrise).<br /><br />It is true that the lower your drive, the more drag and loss of top speed you'll have. Problem is, that you're stuck with the installation made by the manufacturer. Unlike outboards, where lifts are available.<br /><br />You may consider a different design drive, but that means plenty of AUD's...<br /><br />45 km/h sounds low. What is your ready-to-go weight?

 

[arfaname]

Re: Where should my cav plate sit in the water on a Volvo Penta 280?

boat and trailer weigh 1980kg combined. The weight on the trailer reg label is 510kg. I therefore assume the boat itself weighs 1470kg.<br /><br />I have not checked the cav plate to be running true with the hull. <br /><br />I will check that<br /><br />I had the same problem on my last boat with an outboard and by raising the outboard it changed the boat completely.

 

[Scaaty]

Re: Where should my cav plate sit in the water on a Volvo Penta 280?

Outdrives are solid mounted, so no way you can change anything. And its a Anti-ventilation plate

 

[arfaname]

Re: Where should my cav plate sit in the water on a Volvo Penta 280?

Why anti ventilation plate??? what is it stopping from being ventilated?<br /><br />cavitation is caused by the prop pulling air down from the top so is it the same thing??? <br /><br /><br />regards<br /><br /><br />Sean

 

[Dunaruna]

Re: Where should my cav plate sit in the water on a Volvo Penta 280?

No, not the same thing. Ventilation is when air is introduced to the prop from above the waterline, hence the need for an anti-ventilation plate.<br /><br />Cavitation is when the shape of the prop causes water to boil and produce vapor, this leaves burn marks on the prop, literally.

 

[Scaaty]

Re: Where should my cav plate sit in the water on a Volvo Penta 280?

Originally posted by arfaname:<br /> Why anti ventilation plate??? what is it stopping from being ventilated?Sean

It you did not have that plate there, you would have a sideways roostertail where the thrust would break the surface tension. And any manual will call it that.

 

[arfaname]

Re: Where should my cav plate sit in the water on a Volvo Penta 280?

"I see i see said the blind man" , when he really didnt see at all. <br /><br />All makes sense now and thanks for the heads up this arvo Aldo. <br /><br />I guess the term cavitation plate comes from having owned ski boats in the past.