Cavitating motor

[Crump]

I have just purchased a Stacer 4.3m Barramaster with a 40hp Johno, while it goes like a cut cat, when tuning at speed, and I dont mean sharp turns either, the motor cavitates.I have removed the Hydrofoil and this made no difference, as well as adjusting the pitch. Any ideas, or is it just an anomaly of this hull/motor combination??

[Roughasguts]

Which way did you adjust the trim?
But yeah it can happen quite easily in tight turns.
Wide turns it shouldn't.

[Crump]

adjusted in all directions and cant get rid of it, but even at speed say along a river,just following the bends it does it, meanwhile the mate with his V hull and 30hp leaves me behind, its a real PITA.

[Kerry]

Take a geek at your keel, especially the last 3-4 feet! What's it do?

[Roughasguts]

Can you easily drop your motor a couple of notches.
The motor may need to go deeper, to get out of the airated, or agitated water caused by the hull and the turn.

I find if I trim in for tight turns i'm less likely to cavitate, also power up a tad before the turn.

That way your less likely to drop so much speed during the turn.

But i'm not familiar with your boat can you describe it,
Flat bottom, tiller steer or C/C how many pony's.
How many bod's on board where do they sit.

[James_Rand]

Crump,

If it is cavitating when navigating the gentle turns in a river, then your motor if trimmed correctly, must be sitting too high.

Amazing the difference dropping or raising a motor one hole can make.

Drop it one hole and test. Hope that helps!
jr/

[davez104]

I have the same dramas with my barra punt. It's a 3.95M Bermuda Discovery with a 40hp Honda. When I bought the boat it had a 50hp Yammie 2 stroke with a permatrim foil and it had no cavitation issues at all, also went like a rocket!! I've tried raising and lowering the moter height on the transom, makes little difference either way, except for a bit more top end speed with the motor up high, so thats where it stayed. I think the cav plate is just above the bottom of the hull at the moment. The prop has seen a fair bit of wear so I am thinking this could be part of the problem but have not yet got as far as replacing it. I have been told that a prop with extra cupping in the blades will help heaps. I also find that the more weight I have up front the better it is.

Dave.

[Crump]

Can you easily drop your motor a couple of notches.
The motor may need to go deeper, to get out of the airated, or agitated water caused by the hull and the turn.

I find if I trim in for tight turns i'm less likely to cavitate, also power up a tad before the turn.

That way your less likely to drop so much speed during the turn.

But i'm not familiar with your boat can you describe it,
Flat bottom, tiller steer or C/C how many pony's.
How many bod's on board where do they sit.

flat bottom V nose, side console, 40hp, just with me in it, and the motor is at its lowest setting.

[Roughasguts]

Crump, does it cavitate more turning to the right? and hardly at all turning to the left.

If so you might need some balance weight opposite to where your sitting.

[Kunnara1]

I have a 4.3 Stacer Proline with a 30 yammie on the back and it has cavitated since it was put on and nothing has been able to stop it.I think its something to do with the hull shape and I just learned to live with it and watch my turns...
Kunnara

[harlequin]

kerry, interested in what your response would have been. also have cavitation on turns 5m plate centre console weight 750 kg 90 hp yamaha on top hole cav plate approx 1" below keel have raised it but cavitates worse, keel is about 1"wide 1/2" deep protrudes past plate bottom for entire length of hull. has two strakes & reverse chine on each side about 4"wide, believe the keel could be the cause of cavitation bubbles trapped down hull exit out rear? is this correct , solution may be weld some plates in from transom, keel back couple feet to flatten it out? all advice appreciated thanx

[fisha63]

kerry, interested in what your response would have been. also have cavitation on turns 5m plate centre console weight 750 kg 90 hp yamaha on top hole cav plate approx 1" below keel have raised it but cavitates worse, keel is about 1"wide 1/2" deep protrudes past plate bottom for entire length of hull. has two strakes & reverse chine on each side about 4"wide, believe the keel could be the cause of cavitation bubbles trapped down hull exit out rear? is this correct , solution may be weld some plates in from transom, keel back couple feet to flatten it out? all advice appreciated thanx


I had the same probs on my hull ...after advice from a few people #I got the grinder and from the transom took 300mm off the keel #and tapered it off.....result...a reduction in ventilation probs by at least 50% might not work for all situations though :)

[Kerry]

kerry, interested in what your response would have been. also have cavitation on turns 5m plate centre console weight 750 kg 90 hp yamaha on top hole cav plate approx 1" below keel have raised it but cavitates worse, keel is about 1"wide 1/2" deep protrudes past plate bottom for entire length of hull. has two strakes & reverse chine on each side about 4"wide, believe the keel could be the cause of cavitation bubbles trapped down hull exit out rear? is this correct , solution may be weld some plates in from transom, keel back couple feet to flatten it out? all advice appreciated thanx

Stacers had (have?) about a 75mm "I" beam keel section and the last 3-4 feet was tapered up to the stern. These designs were extremely efficient had throwing dirty water past the prop. Really the back of many pressed alloy's aren't what one might call favourable in reducing broken water.

Regards, Kerry.

[ahoj]

the rule: place your cavitaion plate 30- 75 mm below your floor when on second notch-- make sure your floor and cav plate are at level at 30-70mm below
Some of us boaties are placing lots of weight up front and make transom jump out of water thus cavitation --Leaving the outboard on first notch and traveling fast will bury your prow and lift transom up...
I have not found yet different makes of motor to be the same size as standard short shaft or long shaft --all different even marginally
Example; Evinrude 6 hp short 45cm
Mercury 6 hp short 47 cm
Evinrude 25 hp long 58 cm
Evinrude 15 hp long 56 cm
Suzuke long 7.5 hp 60 cm

as demonstrated there are indiscrepencies in lenghts and 20 m/m can create a lot of problems

hope some of this info will help-----------------Ahoj --if only marginaly ;D ;D

[Kerry]

ahoj, 25mm below hull level (not keel level) absolute max. No more otherwise drag will simply kill it. In the case of pods then the motor can be lifted 25mm per foot behind the stern proper.

Regards, Kerry.

[harlequin]

thanks for reply fisha63, kerry reckon i will take the grinder with flap disc to the keel blend it back 300mm or so be the quickest easiest solution