Why am I ventilating?

[Gus Mortimer]

This is a 16' Conroy (glastron) with an 82 90h mercury 19p alum 3blade. the problem(prop blowout)does not happen very often, and seems to be when heavely loaded, sometimes, or when cornering sharply, sometimes. <br /> I have a theory that air is forming around the prop due to a bent skeg. My skeg bends to the right so to counteract the turning I adjusted my anode tab left. I am just guessing but do you think by "forcing" the engine to track foward like this it creates air in front of the prop?

 

[Chris1956]

Re: Why am I ventilating?

Jr, I do not think the cause of your ventilation is a bent skeg. I think you should see where the antiventilation plate is with relation to the bottom of the boat. If the A-V plate is more than 1/2" above the bottom of the hull, the motor may be mounted too high, and should be lowered. Also, boed that boat have a keel which interrupts the flow of water to the prop?

 

[wvit100]

Re: Why am I ventilating?

In a tight turn the prop will always blow out unless you trim down and reduce throttle. Also if you hammer the power and the prop cannot keep it's bit on the water it will cavitate. Cavitation is where the vacuum caused by the prop is low enough to cause the water to boil. The boat is heavy and can't get moving fast enough to keep up with the engine so something has to slip. Kind of like spinning the tires on a car.

 

[MrBill]

Re: Why am I ventilating?

jr: the skeg and anode tab have little or nothing to do with prop blow out, unless the skeg is severely deformed. The anode tab counteracts forces resulting from prop rotation, it is unnecessary with power steering. As Chris1956 suggested, your problem is likely due to A-V plate height and/or the naturnal cavitation resulting in a tight turn.

 

[LubeDude]

Re: Why am I ventilating?

You probably just need to get used to your boat more, you may not have enough cup on your prop, You didnt give us your WOT RPM #s, but you could maybe go to a fourblade 17P which would also help.

 

[Gus Mortimer]

Re: Why am I ventilating?

the AV plate is perfectly flush with bottom of transom. there is no keel. I am not sure how bad you mean when you(mrbill) say severly deformed, but it is bent to the right 3/4 of an inch or more. before adjusting the anode tab it would make a hard right if you let go of the wheel and was very difficult to turn left(not power steering). <br />As for the WOT rpms I dont trust my tachometer. usually it says 4400, sometimes(with no difference in sound) it will say 5000. The reason I got concerned is that it happen the other day with a full load just going along in a straight line. I had to throttle off plane and then take off again to get it to stop. I wa worried that it had slipped a gear or something but other than the increase in RPM I heard no noises at all and my lower seems fine on inspection out of the water.

 

[Chris1956]

Re: Why am I ventilating?

JR. My speedboat pulls right when the trim is down, steers neutral when trimmed moderately and pulls left when trim is maximum. Your bent skeg may add to the pulling right, and your best bet is to adjust the anode left(CCW from above) to compensate. Now as to why the prop blewout while travelling straight. No easy answers come to mind. Some v-hulls rise straight up as speed increases. I had a 16' runabout with a straight vee hull. The faster it went, the more it rose. Eventually the prop would ventilate. Luckily for me I was too afraid to to WOT with that boat/motor combination - I thought it would self-destruct <br /><br />Seriously, If the boat ventilation is related to current speed, you may have to lower the motor height on the transom. If not, maybe the hub is slipping or the boat is loaded with too much weight forward.