Characteristics of 3 vs 4 blade props

[bigpat]

Hi all,

Just wondering if people can confirm the differences in boat performance between 3 and 4 blade props.

Is is correct that changing from 3-4 blades in the same pitch will reduce rpm by 500 rpm?

For same performance ( and WOT rpm) you need to drop back 2 inches of pitch with a 4 blade?

That a 4 blade will consistently lift the stern higher than a 3 blade when up on the plane?

With a 220 kg Honda on the back she does ride nose up at speed.

I run a Mercury 15 p Black Max prop for 5800rpm WOT.

Just curious as I want to get the best performance out of her....

Thanks in advance,

Pat

[Malcolm W]

I switched from 3 to 4, used Solas to play around with the prop size and engine height. My problem was ventilation although the 115 Yamaha 2 stoke was at the correct revs with the standard 3 blade prop. Going to a 4 blade enabled me to raise the motor 2 notches with no ventilation. I ended up with the same pitch and diameter, with the raising of the motor each notch gave me a 200rpm increase, back to the original rpm. The 4 blade does take more torque to run, keep that in mind as every motor 2-4 stroke have different torque levels.

I will try and answer your questions in red.




Is is correct that changing from 3-4 blades in the same pitch will reduce rpm by 500 rpm? Mine reduced approx 400rpm

For same performance ( and WOT rpm) you need to drop back 2 inches of pitch with a 4 blade? I would say more, I tried a pitch lower (engine at the same height) and didn't reach the same revs as the 3 blade. You already have a fairly low pitch at 15 though.

That a 4 blade will consistently lift the stern higher than a 3 blade when up on the plane? My boat does, but as I was able to lift the motor 2 notches i think that helped also.

With a 220 kg Honda on the back she does ride nose up at speed. Perhaps a foil or trim tabs?

I run a Mercury 15 p Black Max prop for 5800rpm WOT. Mercury are a good prop, the revs look ok. Id try the simple things first, like distributing weight to the front?

[Noelm]

go to your nearest Mercury dealer and get one of their propeller brochures, (free) it explains everything about how they work in quite good detail.

[rexaway123]

I agree with what you say.. I went down from standard 19 to 17 pitch when went from 3 blade to 4 blade to keep up RPM on my twin 150 4s yammies on back of 2300 Noosacat...notice was HUGE in terms of stern lift ( as they are marketed as doing!) so much so that first time out I felt the nose start to plough when I planted the throttle with trim down....where used to lift... now I plant throttle with trim a few bars up and nose does not even lift boat rips up speed staying dead level lifting its HEAVY bum up easily and staying there at lower RPM

my REP imported these ones for me from US as test and they were successful, can be matched to other motors too
http://www.boatownersworld.com/Props/turbo/turbo_os1.htm

[WalrusLike]

In Sunday in the washing machine at the Brisbane Bar I found that full throttle wouldn't push me out of the way of the following sea.

I can't afford to upgrade motor so maybe 4 blade would've helped there.

Two times I was bogged in an uncomfortable situation that needed a bit more punch. It's probably time to go prop hunting.


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[bobbyb]

I love my 4 blade solas s/s prop I imported from USA, cost me $400 bucks butt is a gamble as to weather it's the rite one or not.....

anyway the 17p was a bit over propped for my 150 so I imported the same prop in a 15p to lift the rev a bit more and couldn't be happier.

so now I'm left with 14 1/2 x 17p solas 4 blade s/s prop ( as new)

if any ones interested give me a bell, no use to me.....:)

[WalrusLike]

Bobby I might have been interested but I think I need to go down in pitch if I go up in blades.

Currently have the alloy 17K. Can't see any other markings.


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[Giffo65]

Pat
Funny you should post this ,as you know we have almost identical setups.I bought a 13.5 x 15 - 4 blade prop today off the net.I will see how it goes when it gets here in a few weeks.My old Cruisecraft is bum heavy with the Honda 130,looking for lift.Trim tabs is next maybe.

[Darren Mc]

Just curious bigpat, what diameter is your mercury 15p and what hp Honda are we talking about? You may be able to keep the same pitch but come down in diameter to keep approx the same rpm. Diameter and pitch go hand in hand, one being as important as the other. In my experience yes you do need to come down 2 or more pitch to keep the same rpm, but if your merc prop is huge in diameter that might be why it had to be such a low pitch to get those rpm's.
Spaniard king would be a good person to talk to for anything to do with Honda's and setting them up with the correct prop.

[Darren Mc]

That prop should go well on your boat Giffo65.

[Giffo65]

Darren

I tried a 13.5 x 16 at the 1770 M&G and it made a difference over the 17 that is on it. Should be interesting with the 4 blade Murf said it changed his boat totally.

[lucee81]

i noticed when i went to a 4 blade solas prop on a 04 yammie 2 stroke 90hp that i went down 2 pitch sizes to get close to the same revs however speed has been compromised in a big way lost about 15kmh and that was with a fooked 3 blade, i have since put the 3 blade back on and get about 65kmh and about 50kmh with the 4 blade
fuel usage with the 3 blade , a trip to mud island from Whyte island cost about 30lts of fuel
fuel usage with the 4 blade, same trip as above cost about 25lts of fuel
fuel usage taken from EPR60 fuel monitoring system.

[bigpat]

Thanks for the replies! I like the idea of stern lift, make the boat easier to trim. Trim tabs are on the wish list too, at the moment I want to try and optimise what I have....

Giffo, by all means let us know how you go! Pick up the prop at a good price I gather?

By the way, my engine is a BF130. The prop is 13.75 x 15p.....

[Giffo65]

Yes Pat, 190 bucks delivered from the states,it is second hand but had little use.

[Spaniard_King]

Yes Pat, 190 bucks delivered from the states,it is second hand but had little use.

Geez there wasn't even a beer in that line above for the spotter :(;)

[Giffo65]

Yes I should mention, Garry put me onto it,a bargain. Thanks :thumbsup:

[bigpat]

Speaking of which, I wonder what's the guru's opinion on whether I need a 4 blader????

[Spaniard_King]

Pat your figures are pretty close too the money.

you would loose top end rpm with a 4 blade 15 IMO.

What do you want to achieve? Some things are only acheiveable with more HP

[bigpat]

Hi Garry,
I would like to get the bum up out the water, as after thinking about it, I use a fair bit of negative trim on it on the plane.

From a 15p 3 blade, would I go to 4 blader of say 13 or 14 pitch?

I see the Solas 4 bladders have a high rake, which assists stern lift, no way I could put a 15 incher you think?

Would love a 150 hp, but don't have a spare $20k.....

[Fed]

Most boats perform best with 3 blade props.

[Jarrah Jack]

Pat
Funny you should post this ,as you know we have almost identical setups.I bought a 13.5 x 15 - 4 blade prop today off the net.I will see how it goes when it gets here in a few weeks.My old Cruisecraft is bum heavy with the Honda 130,looking for lift.Trim tabs is next maybe.

You would find that the tab's will make a big difference even if the new prop works well. I know of someone with the same boat as your's and after a few mods to the transom couldn't get up on the plane until he added tab's.

[gofishin]

Most boats perform best with 3 blade props. Don't know whether I would say "most" Fed.

It also depends on how one defines 'performance', and what one is prepared to accept if a trade-off has to be made...

Do you want top end speed, mid range speed and/or economy, holding power in the big stuff, transom lift, low speed manoeuvrability etc etc...

Some boats love 4 blades, others don't. Same for skippers. There are also other considerations with 4 blade props, as they are generally heavier and have much better low speed grip than a 3 blade, and hence impart more inertia forces on to the g/box drive train etc.

Some boats perform best with 4 blades, others don't. One prop (3 or 4 bld) may perform great on one boat, but poorly on another. Unfortunately it is trial and error unless you can find someone with your combo that has done it all before and documented it well enough for you to make a judgement.

Importantly, get your motor height right. IF you find a particular 4 blade works well for you, you can normally go up one hole higher than for a 3 blade, as they 'generally' provide better grip.

Here are a few post/links that might give some more info. There will be dozens of others if you search etc, just remember these ones easily.

Bit big in diameter & pitch for your needs, but if anyone else is interested I have an 'as-new' PowerTech ELE 15" x 17"p 4 blade (with FloTorque hub) I will shortly be putting in the classifieds when I get off my backside. It doesn't work well enough for me, and has been collecting dust for a while.

cheers
Brendon




http://www.ausfish.com.au/vforum/showthread.php?189702-Seeking-Prop-Advice-Please&highlight=diameter

http://www.ausfish.com.au/vforum/showthread.php?156703-3-blade-vs-4-blade-props-–-Outsider-685-F250&highlight=blade

http://www.ausfish.com.au/vforum/showthread.php?157181-CC-Outsider-625-3-blade-vs-4-blade-prop-trials-–-ROUND-1&highlight=blade

[Giffo65]

Jarrah Jack
I hope you had a good trip home from 1770,bit of a haul for you.
As you are aware of the trim tabs conversation at 1770,It is a consideration of mine,everyone that has installed them loves them.The person that fitted the tabs with similar boat to mine,if I pm my number to you ,would they give me a call or I could call them for a chat ?

[Spaniard_King]

Don't know whether I would say "most" Fed.

It also depends on how one defines 'performance', and what one is prepared to accept if a trade-off has to be made...

Do you want top end speed, mid range speed and/or economy, holding power in the big stuff, transom lift, low speed manoeuvrability etc etc...

Some boats love 4 blades, others don't. Same for skippers. There are also other considerations with 4 blade props, as they are generally heavier and have much better low speed grip than a 3 blade, and hence impart more inertia forces on to the g/box drive train etc.

Some boats perform best with 4 blades, others don't. One prop (3 or 4 bld) may perform great on one boat, but poorly on another. Unfortunately it is trial and error unless you can find someone with your combo that has done it all before and documented it well enough for you to make a judgement.

Importantly, get your motor height right. IF you find a particular 4 blade works well for you, you can normally go up one hole higher than for a 3 blade, as they 'generally' provide better grip.

Here are a few post/links that might give some more info. There will be dozens of others if you search etc, just remember these ones easily.

Bit big in diameter & pitch for your needs, but if anyone else is interested I have an 'as-new' PowerTech ELE 15" x 17"p 4 blade (with FloTorque hub) I will shortly be putting in the classifieds when I get off my backside. It doesn't work well enough for me, and has been collecting dust for a while.

cheers
Brendon




http://www.ausfish.com.au/vforum/showthread.php?189702-Seeking-Prop-Advice-Please&highlight=diameter

http://www.ausfish.com.au/vforum/showthread.php?156703-3-blade-vs-4-blade-props-–-Outsider-685-F250&highlight=blade

http://www.ausfish.com.au/vforum/showthread.php?157181-CC-Outsider-625-3-blade-vs-4-blade-prop-trials-–-ROUND-1&highlight=blade

Brendon,

Pm me with a price, I think I can move it for you

[WalrusLike]

Do all prop brands have same shaft diam and splines etc? So they are interchangeable?

My Yamaha 3 blade was 'bogged' twice in waves at Brisbane Bar.... not enough bite to get me out of the way of a following sea even at full throttle.

I think from the above discussions a 4 blade might give me more torque in that situation and I don't mind loosing top speed especially if cruise is more economical.

Mine is a 13x17K Yamaha on a 115 2stroke.

Am I correct that I would need a 13x15? I can't find what the K means.... something to do with metal used? I am a bit reluctant to contact Solas because I am a easy sale and I can't really afford a new one.... Looking for a trade or a secondhand one so its not so dear.


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[hilta1]

I put 4 bladers on the 115 yammis on the cat, made a huge difference, I have the 3 blade stainless ones that I would sell if anyone interested,1 is counter rotater, 3 bladers work well on the other boats we have,never had a need to try 4 blades on them but would be an interesting exercise.

[Darren Mc]

Hey WalrusLike,
I've got a 115 Yamaha 4 stroke on my baysport 585 and I had exactly the same prop as you have, the 13 x 17k. I bought a solas 13 1/4 x 15R SS 4 Blade from the US and my wot rpm dropped from 6000 to 5800 and I can still get about 33 knots out of her. It's a huge improvement over what I had and cruise economy is good to, around the 2.1 km per lt.
It plane's as low as 3700rpm and get's up on the plane heaps easier and quicker. Prop slip is barely noticeable at all as it has heaps more grip.
I am very happy with the way the boat drives now and wouldn't go back to that crappy 13 x 17k if you paid me to.
I reckon the 13 1/4 x 15R 4 blade would be the size for your boat too. If anything it would probably go better than mine being a 2 stroke with a bit more punch.
I paid $ 311.15 delivered to my door in about 3 weeks.

Cheers mate.

[WalrusLike]

Wow thanks. That's basically the same hull (maybe exactly) so it is a good bet mine would love that prop too.

Excellent help and that price is about the top of what I can afford to do. Thanks heaps.

Would you please consider pm me the supplier? Thanks for your advice.


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[WalrusLike]

Hey really dumb question fellas... Am I right in assuming my prop is a Right Hand pitch?


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[Malcolm W]

Walrus, don't forget Darren has the 115 4 stroke, it's lower geared. 2.15 - 1 v 2.0 - 1. Before you order, consider the prop size 13 1/4 X 15 may be a little over propped. The four strokes are generally lower geared than the 2s and will rev higher. 5000-5500 max HP for the 2 and 5500-6000 for the 4.

After doing this exact thing to my 115 2 stroke, I agree with Darren the standard 13x17 Yamaha prop is ordinary, but I think just drop the pitch down (15 or 13). Better off with the revs up in the higher range than overloading the motor. It's a pity you are on the other side of the country, as you could borrow mine and go from there. I feel mine is slightly over propped with a heavy load (13x17) in a plate ali.

If your motor is standard it will be right hand pitch, just look at the prop and if it needs to go right hand down as you face it to push the boat. Counter rotating are mainly for cat's and are left hand down.

[bobbyb]

while the rite prop is important it can still only achieve so much... 8 out of 10 boats out there are under powered (IMO)

I think boat manufactures and sales yards have a lot to answer for. totally ruining a boats performance for the sake of making the sale prise a bit cheaper with a under size motor. my thoughts only.....

[FNQCairns]

Anyone want to sell me their old 13x17 yam prop.

[WalrusLike]

Mal thanks for that... I didn't realise the gearing was different.

Darren said his pitch is 15p maybe a 14 for me?? I will check it out. I think the Solas prop finder said a 13 1/4 x 15p Stainless

Bobby I agree... Mine is at bottom of acceptable power I think.

FNQ if noone else gets back to you I will have a prop for sale in about a month. Don't know what the Yammie prop is worth... Probably about $1000?? :)


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[Gon Fishun]

Walruslike, I have a 4 blade 13" diam x 15 pitch x 13 spline aluminium blade that I use for towing the tube. You are welcome to borrow it ( if it will fit) to see if those specs are any good. You would have to pick it up from Woodford tho, or I might be able to drop it into Caboolture, Bribie? somewhere?.
Cheers, Bob.

[FNQCairns]

FNQ if noone else gets back to you I will have a prop for sale in about a month. Don't know what the Yammie prop is worth... Probably about $1000?? :)



1000$! one the Queen Marys might be a little large for my boat..:)

[hilta1]

I would consider selling my 13 x17 stainless yammi prop,pm me with an offer, not sure wether to split them as 1 is counter rotater, in perfect condition,. cheers Mark