3 blade Vs. 4 blade

[whistlevapour]

I am curious to what are the main affects which a three blade has in comparison to a four blade.

[imq707s]

It all depends on what kind of prop it is. One thing that I've found to be true no matter what prop is that 4-blades seem smoother than 3-blades....they send less vibration back through the steering wheel.

[whistlevapour]

do they affect the performance in any way other than that

[Trikki1010]

4 blades will be generally slower rpm for rpm due to additional drag and additional weight of the 4th blade.

But, what the 4 blade gives you is two blades in the water at any one time, whereas the 3 blade has only 1/2 of two blades or one in the water at any given time....thus is why the bow hunts alot with 3 blades while the 4's are inherantly more stable....

Than again, the above is based on optimal set-up as to height & RPM's in a surfacing or semi-surfacing applications.......;)

[imq707s]

It all depends. Some 4-blades give tons of lift (like a Trophy), but some that I have tried dont (like a shooter). Some 4-blades I've tried grip really good out of the hole (shooter), and some slip like crazy (renegade). Different props do different things....4 or 3 blades.

Some boats run better with a 4-blade....while others like 3 blades.

What kind of boat do you have, what is your setup, and what props are you wanting to try out?

[whistlevapour]

Its a Glastron Carlson cv 16-ss on a 2.5tdi land rover engine (200tdi) and is on an alpha 1 diesel leg on a 2:1 ratio. A bizzare project but the old petrol is a bit pricey in Ireland! But we were recommended a 30/32 pitch as the revs are low.

[k-man]

give john janacky a call - he will definantly try to get what your lookn for - 1-262 - 534 - 4440 - if ya want top speed a 30 raker sounds like what your lookn for - but he's the expert & a call worth making - good luck - k-man

[imq707s]

With a sterndrive setup like that….I would start out with a 3-blade if you are looking for max top end in smooth water. If you are running in rough water or are planning on carrying heavy loads around, I would start out with a 4-blade. Got any pics???

[whistlevapour]

Here she is!

[whistlevapour]

I'll try and get more it won't let me put on higher quality. Do you know anything about putting a mazco prop on an alpha 1 leg? Will it matter with out the exhaust hub on it.

[staylor]

I think you'd be best off trying some plain old 3 blade aluminum props just to baseline your performance. With as much weight as you've got aft I don't think you should run anything but a through hub prop if you've got the exhaust routed through the lower unit. A very quick off the wall guess is to start with about 19-21 inch pitch.
Doug

[whistlevapour]

We have a 3 blade 14 1/2 X 27 aluminium and it tops out in very very little time. Its low revs and torquey enough. It was toppin out easily because it only revs to 3800 on a 2:1 ratio. Would not having an exhaust hub have a major effect on an alpha leg as the exhaust runs down the leg in ours.

[Trikki1010]

Here she is!

No offense, that doesn't lool like a 16' Glastron :confused:

[whistlevapour]

It's a 1973 there doesn't tend to be too many around!

[staylor]

...I show the Rover 200 at 107hp @3800 rpm. With the 27 inch prop at 3800 rpm this works out to about 43 mph. I don't know if 107 hp is going to do much better than that on your rig. Are you able to over-rev above 3800- indicating that you need more pitch? If so, you'll never spin a 30 inch over the hub, and it's not worth the effort to convert the exhaust to anything other than thru the leg. If you're not able to over-rev, then you're probably propped as good as you can be. The only other option is to see if you can swap to a different gear set. I know that Alpha drives come in 2:1 for the small engines, with larger engines running 1.62:1 and possibly 1.81:1 ratios. If it is possible to swap the gearsets, then this may be a better and less costly solution than getting into a high cost specialty prop.
Doug

[whistlevapour]

It tops out very easily but I've found a prop alright I think!

[whistlevapour]

Its got plenty of torque though its hitting 255 N/m at 1800 rpm. It would be on the plane at that stage

[whistlevapour]

would a bravo1 prop fit onto an alpha 1 leg? Cause one person just said it would and then another just came along and said it wouldn't!