Prop advice needed

[Cdn20valve]

Hey guys,

I have a 26 footer pocket cruiser. Donzi LXC 255. Bravo 1 drive. 5.7 Carb

was running a 17 pitch 3 blade stainless prop. ran fine, but thought I could get a higher cruising speed. So i installed a used 19 pitch 3 blade stainless. Went out for first run. Cant get on plane unless move all weight to bow. Once on plane, I got more speed out of it. But the holeshot is non existent.

Thinking of getting a 4 blade 18 pitch. would like better holeshot and higher cruising speed. What are your thoughts?

 

[jimmbo]

What RPMs were you getting at WOT with the 17in. and with the 19in? What is the WOT Range of your Engine?

 

[Cdn20valve]

My engine should go to 4800.

I hit 4400 with the 17p. I should add that my tach is a little wonky. I have to tap it. So not sure if 4400 is accurate.

Less with the 19p. It was struggling to keep on plane unless wot.

 

[jimmbo]

4400 is usually the bottom end of the RPM range for any engine since the late 80s, so a 17 is already pushing it loadwise. 19 is too much pitch and you risk melting a Piston.

 

[Scott06]

My engine should go to 4800.

I hit 4400 with the 17p. I should add that my tach is a little wonky. I have to tap it. So not sure if 4400 is accurate.

Less with the 19p. It was struggling to keep on plane unless wot.

Fix your tach or verify correct WOT before playing with props. Obviously 19" is too much pitch and you are lugging the engine. If 4400 was indeed accurate you should be going down in pitch not up

A 4 blade will help with stern lift, hole shot, and lower planning speed. Props are trade offs if you want better holeshot you will loose not gain cruising speed unless you have a bigger engine.

 

[Cdn20valve]

4400 is usually the bottom end of the RPM range for any engine since the late 80s, so a 17 is already pushing it loadwise. 19 is too much pitch and you risk melting a Piston.

Ok, so I should be looking at 15 or 16 pitch? what if I were to go 4 blade? should I go 16 or 17 etc...

 

[Cdn20valve]

Fix your tach or verify correct WOT before playing with props. Obviously 19" is too much pitch and you are lugging the engine. If 4400 was indeed accurate you should be going down in pitch not up

A 4 blade will help with stern lift, hole shot, and lower planning speed. Props are trade offs if you want better holeshot you will loose not gain cruising speed unless you have a bigger engine.

4 blade sounds like the best for my heavy ass boat.

I should fix my tach. its on my list.

 

[jimmbo]

A 3 blade 15 should bring it up to 4800. If you want to really kill your speed, a 4 blade is the way to go. And you will need to go even lower in pitch. As for Lower Planing Speeds, a Prop doesn't change the Planing speed of a Boat, that is determined by the Hull. The Bow can be forced down with either Trim Tabs on the Hull, and/or Trimming the Engine/Outdrive all the way in. The hull in not planing in either case, but is moving a long with a forced Down Bow. There are many 3 Blade Props that are Stern Lifters, the Props often look like this. The Prop pictured is a Cleaver Blade, and were used on the Tunnel Racing Hulls, the Drivers had to keep the Bow down at Speed. However even with these, the Boats used to flip over Backwards all too often. My self I prefer Bow Lifters, and would love to see 2blade props for my I/O. I am willing to sacrifice some Holeshot to gain a few MPH

 

[Faztbullet]

Thats a Mercruiser/Outboard thru hub cleaver..below is a racing cleaver for tunnels . They are usually 10.5 to 11" in diameter and run with 1 blade in water. The B1 drive has a lot of drag and best to use biggest diameter prop you can get.

 

[jimmbo]

In the 70s, when the V6 Outboards were introduced the Thru Hub Cleavers props were used on a lot of Racing Hulls as there weren't many Over Hub props out there back then

 

[Faztbullet]

Naaa...just had to go to the right place to get em. No thru hubs raced in the Mod VP or F1 Tunnel series.

 

[Scott Danforth]

. would like better holeshot and higher cruising speed. What are your thoughts?

you cant get both with a prop

to get a better hole shot, you need to go down in pitch

to get a higher cruising speed, you need to go up in motor hp, change gears and go higher in pitch

 

[Faztbullet]

Look over on Ebay and find ya a torque shift prop..it will blast ya out of the hole and depending on cam you can set top end pitch.

 

[jimmbo]

Those things didn't last long, in use, or on the Market. Probably shredded a few Gearcases

 

[Cdn20valve]

So just so I understand. I should just keep the 17p 3 blade stainless. BUT if I want a lower cruising/planing speed, i could buy a 4 blade prop. Do I buy a 17P 4 blade, or drop it down to 16? I see lots of 14.5 x18 4 blades available, but it probably wont work well with my boat.

 

[Cdn20valve]

Look over on Ebay and find ya a torque shift prop..it will blast ya out of the hole and depending on cam you can set top end pitch.

That would be insane in my boat.

 

[Faztbullet]

Those things didn't last long, in use, or on the Market. Probably shredded a few Gearcases

Working at the nations largest HydraSport and Checkmate dealer in the 80's, we sold several hundred of these and never had a gearcase fail. Being the shop foreman and lead tech I set all of the Checkmates up for max performance. Only problem we had from these props(TS and Merc's Version) was busted springs.

 

[velociraptorfarmer]

So just so I understand. I should just keep the 17p 3 blade stainless. BUT if I want a lower cruising/planing speed, i could buy a 4 blade prop. Do I buy a 17P 4 blade, or drop it down to 16? I see lots of 14.5 x18 4 blades available, but it probably wont work well with my boat.

If you want to try a 4 blade, you need to drop 1-2" of pitch when you do so. A 4 blade is going to have more drag and cause you to run lower WOT rpm vs an equivalent 3 blade.

If I were you, and that 4400rpm on a 17" 3 blade stainless prop ends up being accurate, I'd be trying a 4 blade 15" or 3 blade 15" prop.