Test Results

[Waco]

In a previous post (i couldn't find) I mentioned that my motor was throwing rooster tails. Someone suggested that I raise my motor so that the cavitation plate would be even with the bottom of the hull,(which was about 3 inches below hull line) so I did. I did a test run this weekend and noticed a couple changes. Here they are: 1) water pressure dropped considerably while @ WOT, but returned to normal at idle. 2)RPMs did increase, but not considerably (1-200).3)Rooster tail did go away. I would guess that the water pressure would be the most important aspect, so should I lower my engine back down? It did not lose water pressure @WOT before I raised it.

 

[G. Patton]

Re: Test Results

Waco.... That cavitation plate "Should Not Be" even with the bottom (keel) of the boat. At that setting, the water pump would operate normally at idle, but as throttle is applied, the engine raises up of course with the back of the boat, and the water pump will draw air as it is too close to the surface.<br /><br />The three inch (3") setting that you had previously was indeed the reason for the rooster tail problem (too much drag).<br /><br />The proper setting for the cavitation plate is one inch (1") below the keel, and it is to be parallel with the bottom of the boat (Same angle of attack).

 

[JB]

Re: Test Results

I must respectfully disagree with G. Patton. <br /><br />Even with the keel is the lowest proper location for the Cav. plate. Many boaters run the cav plate as much as 2" above the keel.<br /><br />Your water pressure issue may be of no importance (I don't know) or you may have a serious hook in your keel.<br /><br />I would try a hydrofoil to hold the water flow more down to the uptakes.

 

[Waco]

Re: Test Results

this is flat bottom boat..if that is any consequence.

 

[Bob_VT]

Re: Test Results

What size motor? What size boat? What kind of prop? The roostertail is normally created by a chopper prop (stern lifting) and it is the result of the prop "breaking" the water surface while at WOT. <br /><br />I agree with JB and my boat is set with the cavitation plate 1-1/2" above the hull's bottom. <br /><br />Bob

 

[Fouled Plug]

Re: Test Results

I just moved a Yamaha 90 up the transom 2" on my rig to eliminate the rooster tail. It was set too low in the water, and the lower unit was dragging. The cavitation plate is even with the botom of the boat now, but I may play with jacking it up a bit more. I got rid of the rooster, and picked up a knot or two. No cooling problems at all. What was your initial water pressure reading, and what is it now?

 

[Waco]

Re: Test Results

I dont have a water pressure gauge. Visually I could see the water "dribble" out while at WOT and then as soon as I slowed to idle it would "spray" water.

 

[Dhadley]

Re: Test Results

With my best prop I run the centerline of the propshaft just below the pad (keel) on the Hydrostream and still get 28 to 30 lbs. of water pressure. I think that puts the antiventilation plate and water pump at about 10 to 11 inches up.<br /><br />Just a thought........