Prop blowing out around turns!!

[catfishredneck]

I have a 2001 19cc Promaster Bay Boat that's blowing out around turns. The motor is mounted in the middle hole which doesn't quite put the cavatation plate even with the bottom of the hull. If I drop it down will it help with this issue? I've also heard that cupping the prop will help hold the water better. I'm not sure what that means, could someone explain this to me and do I take it to a prop shop to have it done? I've added a hydrofoil to the motor which helped a little

 

[Bondo]

Re: Prop blowing out around turns!!

I have a 2001 19cc Promaster Bay Boat that's blowing out around turns. The motor is mounted in the middle hole which doesn't quite put the cavatation plate even with the bottom of the hull. If I drop it down will it help with this issue? I've also heard that cupping the prop will help hold the water better. I'm not sure what that means, could someone explain this to me and do I take it to a prop shop to have it done? I've added a hydrofoil to the motor which helped a little

Ayuh,... Ditch the whaletail, 'n drop the motor...
Yes, a propshop can add cup to the prop...
It amounts to curling the ends of the blades abit...

 

[catfishredneck]

Re: Prop blowing out around turns!!

The whale tale gave me the ability to trim the boat till there's only about 1ft of boat in the water so if it doesn't affect the turning, I'd rather keep it. Steering is eaiser and it gave me about 3mph more. Should it cause the motor to blowout more? From what I read, it's supposed to help in that department. Thanks for your info!

 

[Dhadley]

Re: Prop blowing out around turns!!

It depends on which fin you have as to how much it helps or hurts. It also depends on how the motor is mounted. When you say the AV plate isn't quite even with the keel, is it above or below the keel? How much?

The theory of the fin is to allow for a higher X dimension setting thus increasing efficiency. Generally speaking (without knowing which fin you have) if the motor is too low the fin will hurt. We'll assume the AV plate is slightly above the keel since you said it helped.

A lot also depends on what style/brand prop you have and it's condition.

 

[will941s]

Re: Prop blowing out around turns!!

I had one on mine (WAY LESS HP than yours), the one that has two seperate wings that bolt to the anticavitation plate, it was on there when I got the boat. Ran good...took some water to get on plane, but did good. I replaced the foot and never put them back on, motor takes no water to get on plane now, runs faster....taked turns like a champ. Not to mention it does alot better w two people in the boat now. Which fixing that issue all the way will hopefully just require my purchase of a 12p prop. Try some props first, it took me ALOT of makes, models, pitches and styles to get mine where I want it. Just remember....the smallest details of props make HUGE differences in the water.

 

[catfishredneck]

Re: Prop blowing out around turns!!

The av plate is about 1" above the keel of the boat. That's after I dropped the motor all the way down today. I'll have to look at the prop and see what brand and pitch it is tomorrow, however I do know it's stainless. If dropping the motor down didn't do anything I may have to rely on some of you for suggestions. I'll let u know after I run it. Thanks!

 

[Greg Mrozinski]

Re: Prop blowing out around turns!!

Sounds like it should be in the correct position and it should perform better.

 

[Frank Acampora]

Re: Prop blowing out around turns!!

Blowing out is a term that describes the shock wave from the nose of the gearcase expanding to the prop diameter or larger and causing the prop to lose all thrust. It usually happens at high speeds.

VENTILATION is usually the term used when due to the angle of the lower unit in the water, the prop sucks in air and loses thrust during hard turns.

Are you experiencing "Blowout" or "Ventilation?"

SO: If you are experiencing ventilation, have you tried trimming in during turns? Very often when a prop/engine/hull/trim combo is set up for best performance on the straight, it will ventilate on turns. The quick and dirty cure for this is to trim in until the ventilating stops, then when finished the turn, trim out again for best performance.

Cupping refers to a slight turning in of the trailing edge of the prop blade and any prop shop can do it for a nominal charge. Cupped props do tend to "hold" the water better and do relieve some of the ventilating problems but may not cure it completely. Also be aware that cupping your existing prop (if not cupped already) will reduce the RPM at wide open throttle.

 

[captkevin]

Re: Prop blowing out around turns!!

Drop the motor & take off the fin. See how it performs & go from there.
Won't cost you a dime

 

[catfishredneck]

Re: Prop blowing out around turns!!

When put that way I guess I'm experiencing ventilation. At 48mph, I don't think I'm getting a lower unit shockwave!! I've tried trimming in and it helps but I have to put the entire boat back in the water, then it gets hard to turn. Why take off the whale tail? It helps with getting on plane and trim. Do y'all think it's having an adverse effect on the ventilation?

 

[sschefer]

Re: Prop blowing out around turns!!

I'm not familiar with that boat, can you post a pic of the motor and transom. Do you know what a pad is and if so do you know if it has one or is it just a straight V hull. Without a pic, I can't tell for sure but it sounds like the remedy could come in many forms. A vented prop might help, a jack plate would get it into cleaner water. I don't think dropping the motor is going to do much good. It sounds like she's laying over hard in the turns and you're staying hard into the throttle trying to push through it. That whale tale is not designed for power turns and it could be a contributor also. Typically you slow down comming into the turn and then power out of it as the boat comes back upright on the keel. Not as much fun but definitely the cheapest solution.

 

[catfishredneck]

Re: Prop blowing out around turns!!

I dropped the motor down and it helped a good bit but in a hard turn it still vents. The motor is still about 1 1/2 in above the keel of the boat, but without a jack plate, I can't go any lower. The boat has never leaned in the turns, it just rotates around the corners, so if I go to a 4 blade prop it should help right? The boat has a pad and yes it rides on it very well

 

[rrhodes]

Re: Prop blowing out around turns!!

I will add that Smart Tabs will take care of helping you plane out faster and give you a stable ride.

 

[Robbabob]

Re: Prop blowing out around turns!!

I dropped the motor down and it helped a good bit but in a hard turn it still vents. The motor is still about 1 1/2 in above the keel of the boat, but without a jack plate, I can't go any lower. The boat has never leaned in the turns, it just rotates around the corners, so if I go to a 4 blade prop it should help right? The boat has a pad and yes it rides on it very well

Every reference and experience (limited to 2 boats I have owned and several ridden in) all boats will cavitate during a turn at higher speeds. You've already received the "trim in" information.

Be careful you're not trying to adjust for the best of all boating experiences... you'll wind up with having nothing you are happy with. Fast from point A to point B; cool. Want to have great turning at higher speed; great. Want a great hole shot; great. Want top speed; great. You're not going to get all of them. Pick your priority and realize you will sacrifice the others a little.

Let us know your absolute priority and you'll get great feedback! Right now, we're trying to second guess.

Good luck!

 

[jimbo_jwc]

Re: Prop blowing out around turns!!

My old boat 1968 Woodson w/120hp Chysler would do the same as yours after adding whale tail/hyrofoil and it seemed to blow out durring high speed turns 35-40mph . But couldn't go 2mpg of fuel , see over bow for 10 seconds pulling skiers and bad hole shot without skiers with eye to sky but it turned at WOT good .what I gained in fuel economy , hole shot , loss of a few mph was worth it to slow down in fast sharp turn as looking back when kids went down to recover them .

 

[Lyle29464]

Re: Prop blowing out around turns!!

I have always set my motor as high as I could stand. Set so it always vents on a hard turn and often in a moderate turn. just tap the trim down a bit do your turn and trim back up. Maybe slow a few knots. If you really like the stern lift of the tail keep it. But I would try it both ways after you get the engine where you like it. The higher it is set with out venting while traveling in a straight line the faster and more efficient the boat is. My gut tells me you should can the tail raise the engine and trim for the corners. Check your speed before and after.

 

[180shabah]

Re: Prop blowing out around turns!!

...all boats will cavitate during a turn at higher speeds...

Not true. My Mariah suffered horrible ventilation with the stock merc prop - there was no aggressive turning at speed, just couldn't do it. Replaced it with a hustler and ventilation was eliminated. Don't know if it would hold it's bite hard over at WOT, never tried, but it would harder than I could/would need it to.

FWIW - 20* deadrise - no whaletail - no tabs