Need prop advice

[grizzly king]

I presently have a thunderjet 20 Luxor o/s with a 150 hp Yamaha. My existing prop is 14.25 x 17. I can only get about 4800 rpm out of the engine. I personally think my engine is not performing to its potential. What prop changes can I make to help me get more rpm out of my engine thus more performance? Suggestions?


Thanks in advance.

 

[SteelyDan]

Is the yamaha a 2 or 4 stroke? Look in your owners manual for recommended rpm range. If your a 4 stroke I think your in the ballpark from what I can remember. The rule of thumb is if you need to go up in rpm the pitch goes down. 2 inches equals 3 to 400 rpm. As the rpm goes up your top speed will go down.

 

[big.griff]

If it is a 4 stroke, recommended rpm is 5000-6000rpm. Everything I have read, is that you should get as close to 6000rpm as you can. I have a Hewescraft SeaRunner 220 with a 150 that had a Mercury Blackmax 15x17 prop on it and would only get 5600rpm. I just bought a Mercury Enertia 15x15 Stainless prop and I am very happy with it. Got the Rpm up to 5800 and also provided better holeshot, more top speed and less fuel burn!!! Not sure how heavy your thunderjet is but I would think you should have a bit more rpm with that prop.

 

[grizzly king]

Is the yamaha a 2 or 4 stroke? Look in your owners manual for recommended rpm range. If your a 4 stroke I think your in the ballpark from what I can remember. The rule of thumb is if you need to go up in rpm the pitch goes down. 2 inches equals 3 to 400 rpm. As the rpm goes up your top speed will go down.

It is a 4 stroke

 

[the fisherman guy]

Making the move to a stainless prop with the same pitch will make a significant difference, especially with hole shot. Stainless doesn't flex like cast aluminum, so you get better performance out of the premium material.

 

[fishnwhenIcan]

I'm in the same boat, so to speak as you. I have a 21' North River with a Yamaha F150. I'm pulling 5000rpm at 38mph with a 13 3/4" × 19" pitch aluminum prop. I emailed Michigan Wheel with my specs and they recommended I drop down to a 14 3/8" × 15 stainless Apollo. I'd like to go the stainless but don't want to get this wrong. A little worried about dropping 4" of pitch. The boat seems bow heavy and seems to need about 34mph to really get up on step. Problem is a lot of times around 26-27mph is about all the water will permit and my mileage suffers. There is not much in the way of trim to her and the motor is on the lowest hole. Thought about starting a new thead but the recommendations should be similar so why compete. Another prop shop recommended going with a 4 blade but I think that could make it worse. Not sure which way to go now. Any thoughts.

 

[JAC]

I have a 20 thunderjet os with a 150 and a 17p stainless I hit 5600rpm and 44.4mph at 700feet elevation. I think you motor height might be to low.

 

[Sr SQ]

I'm in the same boat, so to speak as you. I have a 21' North River with a Yamaha F150. I'm pulling 5000rpm at 38mph with a 13 3/4" × 19" pitch aluminum prop. I emailed Michigan Wheel with my specs and they recommended I drop down to a 14 3/8" × 15 stainless Apollo. I'd like to go the stainless but don't want to get this wrong. A little worried about dropping 4" of pitch. The boat seems bow heavy and seems to need about 34mph to really get up on step. Problem is a lot of times around 26-27mph is about all the water will permit and my mileage suffers. There is not much in the way of trim to her and the motor is on the lowest hole. Thought about starting a new thead but the recommendations should be similar so why compete. Another prop shop recommended going with a 4 blade but I think that could make it worse. Not sure which way to go now. Any thoughts.

FWIC, your rpm is way to low if you can only hit 5k!! Its not a diesel LOL
My buddies f150s really shined once he propped them to rev 6k when the boat had a light load.

My experience has been good with 4 blade props, they hold better at lower speeds but I have lost a couple mph top end but I have only used mercurys Vensura and revolutions.
The revolution is with out doubt the best I have used, and what I would suggest you try in a 15p

I would say you could easily step down 4", one thing to remember your most efficient rpm will change with the different pitch so its not going to be as bad as you might think.
It will be reving higher at any given mph but will be working less, if that makes sense? Load will kill it quicker than revs.

Phone around, some shops will take your GOLD Visa and let you try a few props on the agreement that you will purchase one.

Jac also correct about hight but I would prop right before messing with the hight if you can see your ventilation plate when up on step.

 

[JAC]

Ya but but often ever hole you lift your motor you gain 200-400 rpm. That boat should have nothing smaller than a 15p on it. Is the bottom clean or is it moored??

 

[fishnwhenIcan]

FYI Grizzly, don't overlook the simple things on yours. The dealer down in California who outfitted my boat for the original owners had my programmable tach set to a wrong pole setting. Mine was reading well over over 6000rpm when I got it. I ended up running a 21" for a short time. The tach failed and when i replaced it I checked the setting with Faria and sure enough they put it in wrong. I set it properly and then was only seeing 4400rpm. Then this weekend a buddy noticed they also installed the remote tilt control for the Panther so it was blocking it from getting full throttle. Now, I get 5000rpm, but I shake my head at how they outfitted some things. Make sure you are getting full thottle. With a 17 you should be getting more rpm than me.

 

[fishnwhenIcan]

FWIC, your rpm is way to low if you can only hit 5k!! Its not a diesel LOL
My buddies f150s really shined once he propped them to rev 6k when the boat had a light load.

My experience has been good with 4 blade props, they hold better at lower speeds but I have lost a couple mph top end but I have only used mercurys Vensura and revolutions.
The revolution is with out doubt the best I have used, and what I would suggest you try in a 15p

I would say you could easily step down 4", one thing to remember your most efficient rpm will change with the different pitch so its not going to be as bad as you might think.
It will be reving higher at any given mph but will be working less, if that makes sense? Load will kill it quicker than revs.

Phone around, some shops will take your GOLD Visa and let you try a few props on the agreement that you will purchase one.

Jac also correct about hight but I would prop right before messing with the hight if you can see your ventilation plate when up on step.

I think JAC was responding to Grizzly's boat. Mines on the bottom hole but I have very little room to trim out before I start to cavitate so it can't go up. Would going down in pitch help or hurt me with bow lift. I could use some. Torn betwwen the 17" and 15 but now leaning to the 15" as long as it doesn't bury my nose more. The Apollo stainless 3 blade props can be had for about half the price of a Merc Stainless. Is there much of a differnce stainless to stainless. Isn't the 4 blade going to lift the stern but bury the nose on my boat?

 

[JAC]

I really like 4 blades and I would buy a aluminum and test it out before you spend the big bucks on the stainless. Not all props have the same amount of engineering so just do a little homework on it before you buy it. Were not running go fast boats here so it's not quite as important to look at cupping and things like that. As long as you can carry a heavy load you have a nice cruising speed and you can hit near the top end of what you brand recommends you should be good to go

 

[fishnwhenIcan]

I really like 4 blades and I would buy a aluminum and test it out before you spend the big bucks on the stainless. Not all props have the same amount of engineering so just do a little homework on it before you buy it. Were not running go fast boats here so it's not quite as important to look at cupping and things like that. As long as you can carry a heavy load you have a nice cruising speed and you can hit near the top end of what you brand recommends you should be good to go

You are probably right. It sounds like I need to get this right with the aluminum first. I'll have some extra props kicking around once I get this figured out. With your guys experience with the 4 blade props what characteristics have you found in the way of how the hull will ride? I know it holds better at lower speeds, is better for heavy loads, is supposed to help with fuel economy etc. But I thought guys were using it to get the stern up and bow down. Is that correct?

 

[JAC]

It's smoother it will have more control in reverse. They are know mostly for the stern lifting which helps carry more weight and stay on step at slower speeds. Do you have trim tabs? I don't on my new boat that will be my next add on

 

[fishnwhenIcan]

It's smoother it will have more control in reverse. They are know mostly for the stern lifting which helps carry more weight and stay on step at slower speeds. Do you have trim tabs? I don't on my new boat that will be my next add on

I'm considering putting tabs on it this winter just to level it out side to side as needed. I think that's all there going to do for my boat. I need to find a way to get the bow up out of the water more at cruising speeds. The boat does not get the economy it should.

 

[JAC]

Have you take out all the stop you really don't need. Also put more weight aft?

 

[fishnwhenIcan]

Have you take out all the stop you really don't need. Also put more weight aft?

There's clothing and life jackets up front that's it. I do usually carry a 1/2 to full load of fuel though as I'm a little paranoid on trusting fuel gauges in boats. That all most bit me one time in Bamfield.

 

[JAC]

Ya don't want to be low on fuel

 

[dwflyrod]

i have a yamaha 225 hp ,i took off a stainless yamaha saltwater series 2 .19 pitch and15 1/4 dia.and replace it with a solas amita3 14.5 dia and a 19 pitch.just to get away from the prop weight taking it in and out of gear.sounds like the lower end was going to blow up.and i only lost 1.5 mph.would like to try a 4 blade

 

[fishin solo]

FWIC try the 4 blade it holds the boat on plain so much nicer then a 3 blade also much smoother ride in my opinion I just switched from a 3blade 21p to 4 blade 19p and its a night and day difference I lost 2mph on top speed but id give that up all day for the improvements that ive gotten from the 4 blade

solo