Should I try a 4 blade prop?

My boat is a '97 Larson 206SEI with a Mercruiser 5.7L and an Alpha 1. The prop is an aluminum 14 1/4 x 19. I've never had a spare prop but I'm thinking I should get one. I thought since I'm buying an other prop maybe I would try a 4 blade. I'm fairly happy with the current prop. It's a Flo-Torq model from Mercury Marine. I would want the new 4 blade to fit the same drive hub.
The reason I might want to try 4 blade is for better hole shot and staying on plane at slower speed.
Do I get a 4 blade with the exact same pitch and diameter? Will it improve the things I want to improve?
The boat is used mainly for cruising and tow sports. We normally don't run any faster than 35 mph even though it will do 47 as currently rigged. I normally have anywhere from 3 to 10 people on board.

Thanks for your help.

Re: Should I try a 4 blade prop?

We need your gear ratio (usually on the outdrive). Your present wot rpm and gps speed.
Usually suggested to drop one inch in pitch when going from 3 to 4 blade but that will depend on your present performance.

Re: Should I try a 4 blade prop?

I looked on the outdrive for the gear ratio. I thought it was on the port side near the top. I don't see anything. If it's under the Mercruiser sticker I hate to scrape off the sticker to see. The current WOT RPM is around 4500 depending on the load in the boat. I don't have a gps but the fastest I've ever had the boat up to by the speedo was 47. I know they are notoriously inaccurate. That was only me, not much fuel, and really smooth water.
I've really never cared how fast I'm going. We just cruise and pull toys.

Re: Should I try a 4 blade prop?

Okay, let's try this again. I got a GPS. I had my current prop professionally reconditioned. It is smooth and painted. I loaded the boat with an average load: 4 adults, 2 children, about 2/3 fuel.
My top speed with the trim all the way down is 32 mph at 4,300 rpm. My top speed trimmed up is 43 mph at 4,600 rpm. The max WOT for this engine acording to the manual is 4,600 rpm.
It seems I proped correctly right now. How do I translate this to the proper 4 blade?
I'm not looking for more speed. I'm looking to have the boat stay on plane at a slower speed and possibly perform better towing tube(s) and other toys.

Re: Should I try a 4 blade prop?

sounds to me like you are propped correctly considering your current load. i havent owned a 4blade prop, but the rule of thumb is to drop 1" in pitch, as stated above. that being said, if you dropped your pitch 2" and went to a 4 blade you would gain 150- 200 rpm wot, lose a few mph's, and you would get a lil better hole shot. you would have to be carefull though because that prop would allow your engine to over rev, which can cause disaster for your engine, if you were out with a lighter load it would exaggerate the rpms.
just gotta be carefull, especially when you are the one being towed on the tube and your buddy is at the controls.

diameter, pitch and number of blades are confusing enough, but you could consider a different rake, cupping and surface area,, but there is no rule of thumb for those, that i'm aware of. it just gets more confusing as you get into those characteristics, and should be left to the pro's to decide. but it sounds like a smaller/ flatter rake would get what you want done all by itself, but im no pro.

if you stay with the same brand/style etc.. as the current prop, it will be easier to compare and see what part of the senario, you should tweak some. if you change manufactures or styles, you will need to experiment further and may not be as easy to get the right prop for your needs on the first try

hope it helps

Re: Should I try a 4 blade prop?

It appears a 18" 4 blade should work for you It should maintain rpm you will likely lose a little top end.
The Solas Amita 4 blade has a good reputation.Typically a 4 blade will improve hoe shot,stay on plane better at reduced throttle,
run smoother,and handle better around the dock.

Re: Should I try a 4 blade prop?

Make sure you get a 4 blade that's made for a sterndrive application rather than an outboard. With an outboard we have the ability to easily raise the motor. The outboard 4 blade props are made to run closer to the surface than the 4 blades made specifically for a sterndrive.

Re: Should I try a 4 blade prop?

I was in the same boat as you.....(bad joke, I know) had a 3 blade that was perfect for my boat, 18' bow rider with a 4 cyl. My WOT was right on the mark and hole shot was okay. I spun the hub in the prop and decided to just buy a new one. I went with the solar amitia with the same pitch. The old one was a 21" and so is the new 4 blade. I lost about 500 rpms, witch was a little more than I expected but I only lost about 1 MPH on the top. What is better for me is the control I gained while pulling tubes a wake boards. The boat planes out smoother and when we just cruise around it dropped the rpms by about 200 at the same previous speed. I guess if i bought another one I would get a 20". There just wasn't near the same selection as a 21" or a 19" Hope this helps.

Re: Should I try a 4 blade prop?

I have a very similar boat 2008 Larson LXI 208. I had a 14.25 X 21 three blade. WOT 4800RPM 59MPH. I wanted a better hole shot and slower on plane speed. I put on Smart tabs and went to a four blade Michigan Wheel appollo Stainless 14 X 20 and it made a big difference. on plane at about 14 MPH vs 20 before and lost topend down to 57MPH. Big difference in plane time also about 50% faster now. I bought the prop on iboats and got a great deal! Saved about $100.00 over retail. Good luck.

Re: Should I try a 4 blade prop?

I recommend the Solas HR Titan SS 14-1/8 X 18 for your application.

Re: Should I try a 4 blade prop?

KD4UPL said:

The prop is an aluminum 14 1/4 x 19.

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jestor68 said:

Solas HR Titan SS 14-1/8 X 18

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Going to a SS prop along with adding another blade will pull down the WOT RPM's too much.


I have an Alpha4 14.5x18 prop on a 140 Mercruiser and like it, better holeshot and low planing speed. It's a stern lifting I/O prop.( I know apples to tangerines comparison...)

Re: Should I try a 4 blade prop?

My testing of these props indicates a reduction in WOT rpm of only 150-200 rpm, compared to an aluminum prop of like size. Since he is getting the maximum rpm now, this reduction will still be within his rpm range; in fact, right in the middle.