View Full Version : 18' Sharkcat motor set-up
seatime
07-08-2006, 11:22 AM
G'Day
Some questions for anyone with a 18' Sharkcat with twin 90's.
Currently running twin Tohatsu 90hp 2 strokes with the out-of-the-box 15" alloy props that will spin out to 6000rpm.
It's got plenty of get up and go, so could these props be too small?
What about S/S 17", would they work better, does anyone allow you to test props?
The Tohatsu manual says around 5500 rpm for top of rev range, so 15" aren't the best prop for a twin OB's, what do you think?
Does anyone have a similar rig?
Also, the cav plate level with the bottom of the hull practice, is it the same with cats as it is with mono hulls?
thanks in advance, Steve.
Noelm
07-08-2006, 11:28 AM
could try the bigger stainless props as they MAY be "just right' as it seems by the manual that you are about 500RPM over maximum, and you can experiment with motor height, on most cats you can go up a hole or two from the cav plate level with the bottom. I guess it is an older model and does not have pods??
seatime
07-08-2006, 11:38 AM
Yeah Noelm, it's the old model, no pods. One prop is damaged so need a new one soon. Anyway to experiment without buying them first?
Raising the motors will lift them off the top of the transom, so it would need to be built-up accordingly. They're on the top hole, so there's plenty of adjustment. At present cav plate is about 2-3" below hull.
Noelm
07-08-2006, 12:53 PM
it does not matter if the motor does not "sit" on top of the transom, as long as the four bolts are in, it will be OK, not too sure about a test with props, but the dealer may be able to help out as it could mean a sale, and two SS props are not cheap.
Noelm
07-08-2006, 12:55 PM
OH 2 to 3 inches seems like a lot to be under bottom of hull, especially on a cat, so try raising it first as you may need to go another size up in SS props.
Mr__Bean
07-08-2006, 01:09 PM
One question before you go up in pitch size.
How well is the current setup able to get you up onto the plane when operating on a single engine?
I would hesitate to go up in pitch if this is marginal.
- Darren
Noelm
07-08-2006, 02:15 PM
I doubt if a single 90 will plane an 18' sharkcat with any size prop.
seatime
07-08-2006, 02:22 PM
Mr Bean, good point, don't know about getting on the plane on one motor, haven't tried it. Though a 15" would be the size to do it.
I do know another sharkcat with pods and 135hp V6 2 strokes won't stay on the plane on 1 motor, it has no hope getting up.
It all works OK the way it is, I reckon it could do better, just don't have anything to compare it to.
Raising the motors will be first option and fix the alloy prop for a spare.
A bit concerned about too high rpm and engine damage over the long term, that's why the query on pitch.
rgds
Noelm
07-08-2006, 03:04 PM
not too sure of the physics involved with cats planing on one motor, I just know that it is not too easy, even with heaps of HP, but one motor of modest size will get you along at a respectable "get home" pace though not planing, been there and tried it with my own cats (and I have had a few) with different engines on them.
seatime
07-08-2006, 05:31 PM
I have read it somewhere, think it was an advert for an alloy cat, they reckoned it would plane on one motor. The example of the 5.6m podded cat with the Mariner 135's is an example of over-powering that doesn't work. I've driven that one a few times and it goes OK too, just not quite right.
It's not imperative to plane on 1 motor, just having another motor is insurance enough.
Looks like some experimenting coming up.
rgds
Homer_Jay
07-08-2006, 07:05 PM
I would talk to the guys from solas props at maroochydore. From what i hear they are pretty good at what they do, and with Kevlar cat , Noosacat and Coastal cat all made on the sunny coast i have no doubt they have had quite a bit to do with cats. Would be worth a try before you race out to buy something just to try.
Aaron
Grand_Marlin
07-08-2006, 07:06 PM
G'day Gelsec,
My 18 footer (560 series) had twin 110 V4 Evinrudes and there is no way it would plane on one motor ... even if you were on the plane and pulled one motor back to neutral, it would still quickly fall off the plane.
I had 17" stainless props and it would do 45kts at 5600 revs (from memory)
Cheers
Pete
Noelm
08-08-2006, 07:59 AM
yep seems to be something to do with the motor not being in the middle, I know single motor cats (with engine in centre) will plane easy with modest HP but on the side no way, kinda strange huh!
Marlin ----- 45 kts??? = 83.5 Km/h= 51 miles sheesh that is fast---
How is your cat project going? I hope you have it ready for the new fishing season thats where the money is
Cheers Ahoj
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