250 HP Tritoon Prop venlilation

[suneshop]

I have a 24' Tritoon 25" outer tubes 26" center tube with lifting strakes.Having ventilation problems.(2012) 250 optimax set in lowest position. 17" pitch Enertia SS. Wot 6000.Top speed with 4 people and coolers all near the rear of the boat. 41 Mph Gps. Wot suggested range 5500-6000. The boat weighs 2700 Lbs Motor 505 Lbs. The problem is I can only run trimmed down (in) fully. Any attempt to trim up causes ventilation. Wondering if a 4 blade would help. I see some 4 blades provide bow lift and some provide stern lift. I was thinking a bow lifting prop would pull the prop deeper and stop the ventilation. But am I thinking backwards.

 

[Levinz11]

Re: 250 HP Tritoon Prop venlilation

What did the dealer or Crest say about the engine shaft length and installation? Do you have the right length motor?

 

[Rancherlee]

Re: 250 HP Tritoon Prop venlilation

My tritoon also only likes to run trimmed in all the way, which is also the fastest position on mine. That is, unless, I have a light load then I can trim WAY out and get an extra 1-2mph out of it with the nose cones way up in the air. I have my vent plate level with the bottom of the center tube, lowering doesn't help any on mine. Been thinking of going 4 blade myself, just to see if I can get more trim range with a load. 41mph sounds pretty low for a performance logged 24' with a 250hp engine, I would be expecting upper 40's with that toon! What's your current pitch so we can figure out the slip percentage?

 

[Rancherlee]

Re: 250 HP Tritoon Prop venlilation

Never mind, I see 17 pitch. With a 1.75 gearcase and 6000rpm limit that prop is good for 55mph, at 41 your seeing almost a 40% slip! You definitely need more bite through either a larger diameter prop, more blades, or longer leg motor. A tritoon with a stainless should be in the 10-15% range for slip with lighter load.

 

[Texasmark]

Re: 250 HP Tritoon Prop venlilation

I looked up your Enertia prop and looks like you got the best for the application From Merc. I didn't see blade cupping in the list of amenities but I didn't download the whole spec sheet either. I'm sure it is, having all the other amenities, but you can check it anyway. See if the trailing edge of the blades, about the last 1/4" of it has a slight bend in it. This reduces slippage under certain operating conditions.

Other thing since rancher ran slippage numbers on your prop so I don't need to, slippage may be due to the porting of the prop. Possibly in your application you don't want the ports. Sooooooo plug them up with a solid plug and that may solve your problem. Ports are primarily used for bass boats getting on plane. You really want a shallow pitched prop to get engine rpms up for a fast hole shot, but you want a lot of pitch when you are on the pad racing your buddy to your honey hole. Porting a high pitched prop gives you the best of both worlds....in that application.

HTH,
Mark

 

[suneshop]

Re: 250 HP Tritoon Prop venlilation

Crest said that is the rite length motor but they could lower the transom this winter at the factory.Also there are solid plugs in the prop. The gear ratio is 1.75 so I think that puts the slip about 26% if I figured correctly. Just wondering if 4 or even 5 blade would help. Haven't had a chance to check if the Enertia is cupped

 

[MaPaHa]

Re: 250 HP Tritoon Prop venlilation

I've got a 24 foot tri-toon with full strakes on all toons and it's powered by a '95 Johnson 150. The guys at Power Tech have been putting one of their 4 blade Off-Shore large dia props on tri-toons and that's what he suggested for me. It also has exhaust ports on it for hole shot. I had enough data for them to make a prop selection and it's about as perfect as you can get. They said it would hold better when trimming and it does.

I should add that in building this motor I installed a 5 inch Bay extension to the motor to make it into a X-long shaft of 25 inches, but the boat is built for 20 inch motors. I added a CMC 5.5 inch jack plate to pull it up to the point I needed. I can trim any reasonable amount without blowing out. I'm running just a hair below 40 mph gps with a couple of people in the boat. I have had a load up front and can trim it to pick them up and get the nose cones out of the water.

I would add a jack plate to get the motor back and it should allow you to drop it down a notch. I would call Power Tech and discuss the right prop style because they have several types of 4 blade props. You are running a larger motor so the hub and dia will most likely be different from mine.

 

[Bamaman1]

Re: 250 HP Tritoon Prop venlilation

I see more 4 blade props on bassboats rather than tritoons. Your Enertia prop is the prop that Mercury uses for its performance tests, and your 17 pitch prop should perform well.

I suggest you post your message on PontoonForums.com. They specialize in pontoon/tritoons, and there is a gentleman on there that tests propellers for engine manufacturers.

My Bennington 24' with a Yamaha F150 is running 40 mph GPS @ 6000 rpm's with a Yamaha Reliance 15 pitch prop and a 2.0:1 gear ratio. I get a little ventilation when I trim the motor up, but none when I trim it down.

Tritoons seem to have a point of no return, and that seems to be about 40 mph. Throw another 100 hp (above a 150 hp), and most boats just get about 3-4 mph. Drag and aerodynamics come into play about then.

Your ventilation dilemma might be solved with a little propeller modification or a $1K hydraulic jack plate. Unfortunately that you cannot just experiment with $500 props, unless you buy from a source that'll let you return props that don't work for you.

 

[MaPaHa]

Re: 250 HP Tritoon Prop venlilation

The hydraulic jack plate is a great suggestion from Bamaman1. By the time I got to the jack plate I had spent my budget and settled for a manual one. I have tried a couple of settings and found one that works for an average of conditions although it would be nice to move it up and down on the fly. The more I think about it and reviewing your rpm / speed performance, I would do the jack plate first to get the motor back and deeper. Jack plates are not advertised nor made to lower motors and you can run into tilt problems if you drop it very much. But, moving it back and down just a notch I think would solve much of your trouble. With the angle of the transom just moving it straight back will make it deeper plus the water rise after it leaves the bottom of the center toon should get your prop in better water.

 

[suneshop]

Re: 250 HP Tritoon Prop venlilation

I tried a 4 blade Vensura 17" ss 37.5 mph gps 6000 rpm the tubes do have some hair on them. Crest reps suggested some type of wedge.

 

[jestor68]

Re: 250 HP Tritoon Prop venlilation

Get your dealer to let you try a 15.5 X 17 Mirage Plus.

 

[john_w]

Re: 250 HP Tritoon Prop venlilation

Get your dealer to let you try a 15.5 X 17 Mirage Plus.

Wondering about the outcome of this. Did you get a 4 blade prop? I'm researching 4 blade SS props on tritoons.

 

[john_w]

Re: 250 HP Tritoon Prop venlilation

I tried a 4 blade Vensura 17" ss 37.5 mph gps 6000 rpm the tubes do have some hair on them. Crest reps suggested some type of wedge.

[sorry I quoted the wrong post] I'm wondering about the outcome. Did you get a 4 blade prop?

 

[suneshop]

Re: 250 HP Tritoon Prop venlilation

I got the thing to run 48 mph GPS one time this season so I think it is close to running as I would like. Four good sized guys on board 40 gal fuel with the 17" p Enertia prop @5900 RPM. Could not duplicate again. I talked to a dude with Bob's machine shop(they sell jack plates) he thought I would better off with a 5" shaft extension kit. Then I could adjust motor mounting point to best performance position.I can't find the kit but was told it is a Mercury part and would not void the warranty.

 

[suneshop]

Re: 250 HP Tritoon Prop venlilation

I ordered a Bay manufacturing 5" extension kit (#613) I plan on raising motor to center set of mounting holes that should lower prop about 3.5" will not know till spring if this will work. I hope it does because the wife thinks I have gone crazy.

 

[suneshop]

Update :joyous: Added the 5" extension kit raised the motor (so the prop is about 1.5" deeper) stayed with the 17" Enertia have complete trim control bow up, bow down, regardless of seating arrangement, big fuel economy improvement and near 50 MPH GPS. Finally got it right very happy.

 

[suneshop]

Sorry :brickouble post