Props size for 70 Yammies on Kevlacat 5.2

[Maccas]

Hey all you Kevlacat 5.2 owners I have just bought a Kevlacat 5.2 with 70 Hp Yamaha 2 strokes on it which have only done 25 hrs (2004 models). The problem is I can only get 5100RPM at WOT (31.7 knots). What size props do most of you guys use for best performance as I think that the motors should rev at 5600 RPM at WOT.

[Blackened]

G'day

Wait for dean1 to answer, you will have your answer in a second

In addition to your props, how is your motor height and what diameter, brand and pitch of prop are you running atm?

Dave

[FNQCairns]

Like Dave says if you can get someone with the identical setup that is working well copying it can save lot's of time and money.

If you are looking to keep the rpm at the speed you have now (sounds good!) your only choice on the surface is to keep the same pitch but reduce diameter.

The easy way is to reduce pitch although more often than not it is an absolute compromise that often achieves not much outside of only one of the possible criteria, depending there are another 2 or 3 criteria left begging.

Cheers fnq

[Maccas]

The props are Solas SS 13 1/4 and the pitch is 17. I have had a look at few threads on the subject on Ausfish as far as motor height goes but the pictures were of Yamaha 4 stroke 60 hp and mine which are XL look about the same height as them. Any ideas?

[FNQCairns]

I am not well versed on cats, if you have 13.25dia ATM I am not sure how trim will be affected choosing less or how important trim is I suspect VERY from what little I understand.

You may need in your instance to go go down 1 in pitch then, 2 down would probably be a mistake. mercury make the vengeance 13 1/8 x 16 might be an option?? and is more than a match for the solas also Solas might have an equivalent as that is what they do.

If you are up to testing just for the hell of it a 13x17 3 blade would be a very good test to try if it came off you would be happy. Dunno which or where you will find them for the johnson through typical channels here in oz though, aftermarket o/s possibly - Michigan match, turning point etc.

Also unless tuning for the last 5% of efficiency which no one does on fishing boats anyway there is a good chance you will find an alum prop that works better straight off the shelf than any SS bought off the shelf and in cost-benefit certainly a alum is the way to go.

With outboard height, the water doesn't care what style of boat hull it is leaving it will conform to physical rules, the difference will be just how far a cat hull rises with speed -the motor height will need to reflect this and be deep enough for the prop to hold purchase on the water at all speeds, sucking it to see will tell all.

cheers fnq

[boatboy50]

Hey Maccas,

Sorry, I havn't got those motors on mine, so can't help with props.

Out of interest, did you buy the one from Sydney which was recently for sale?

How much approx. did you pay for it if you don't mind me asking?

Always good to know the value of our boats.

Regards

Darren

[Dean1]

Hey all you Kevlacat 5.2 owners I have just bought a Kevlacat 5.2 with 70 Hp Yamaha 2 strokes on it which have only done 25 hrs (2004 models). The problem is I can only get 5100RPM at WOT (31.7 knots). What size props do most of you guys use for best performance as I think that the motors should rev at 5600 RPM at WOT.

Hi Maccas i have twin 70's on mine as well. I get about 30kts WOT at about 5500. Im not sure what pitch mine are they arent marked. Im not sure where the numbers are on these ive never had a prop off?? Your getting good top end speed for those revs, it must be very doughy down low?? As for height do you have raised pods? If you can tell me where the pitch would be marked ill find out what mine are and id go same as these as i feel they are spot on

[Maccas]

Thanks for the replies guys.

Hi Dean, I have read a lot of the threads on here about Kevlacat 5.2 on here and have checked out the photos of Johnsant's boat and Gav's boat. My boat does have extended pods for the longer leg motors.I think that my motors are about the same height as Gav's boat but a little lower than John's boat. I can make it one hole higher by drilling new holes but I would like to find out what props work for others before doing that.

The information for pitch and size of a prop is stamped around the hole in the prop where the shaft goes through. You may not see it without removing the prop. This is pretty easy, you just remove the split pin from the nut then remove the nut and washer, then the prop should slide off easily. When you put it back on don't tighten the nut too tight, it just needs to be firm because the split pin stops the nut from coming undone. When you have finished the prop should not have any play on the shaft so take notice how tight the nut is when you remove it. Let me know how you go. By the way are your props alloy or SS ?

cheers,

Maccas

[Maccas]

Darren,

I bought my Kevlacat from a guy in Newcastle. It has a hardtop though not a factory job like yours. It has a full height windscreen so it is like a wheelhouse which is OK for where I fish in south of WA but may be a bit hot for up north. Is this the boat you were talking about or is there another one in Sydney for sale.

cheers,

Maccas

[boatboy50]

Hey Maccas,

Never saw it in person, but i'm sure it's the same boat.

Regards

Darren

[Maccas]

Hey Darren

Send me your email and I'll send you a description etc.

I got your PM but couldn't get it to send back, came up with some error

cheers,

Maccas

[boatboy50]

Hey Maccas,

No dramas. I think you need about 25 posts before you can PM. Maybe that's the problem.

boatboy50@hotmail.com

Regards

Darren