Repowered 5.2 KC with twin 60 suzuki's.

[Danf]

I have finally got my Kevlacat on the water after a lot of research and a lot of hard work I decided to go with twin XL 60 hp suzuki's and i was very impressed with their performance on its first run yesterday. The dealer has installed 14 inch props ( yes i told him that everyone else with the 60 yammies has 15's ) The reason he suggested the 14's is for more punch at the sandy cape bar at the top of Fraser which i will occasionally cross. But there is a long trip up the inside of the island approx 80 km which is normally a smooth run. With the 14's there is a lot of acceleration and the boat hits the rev limiter with in 80 meters with 3 adults and half fuel capacity.


Figures so far with 14' prop are : 4800 rpm = 19 kts
5000 rpm = 22 kts
WOT 6300 rpm = 29 kts.

My question is with 15's how much low down acceleration will i loose ?


There also seems to be a lot of turbulent water around the back of the boat between the 3000 and 4000 rpm mark and it tends to " dig is arse down " pretty bad especially if the motors are not trimmed right in.
Is this normal for a KC ?

I am going to trial the 15's any how, just after peoples thoughts.

Cheers Chris.

Mate, would it be possible for you to post a picture of the dash set up. I am interested to see the gauges setup? Can you trim the motors from the controls as well as the original switches on the dash? Thanks

[Dean1]

Unsure about Chris's setup but normal practice is the controls trim both motors at the same time by pushing the one trim switch and the trim switches (binnacle switches) on the dash allow you to trim each motor seperatly. Thats how mine is set up and this is the correct way otherwise they would been a real pain to operate.

Deano.

[myusernam]

i would be very unhappy having a cruise at such high rpm.
22 knots at 4800 rpm (what the other guys are getting) is the go


As an aside have always thought the 5.2 kevlacats were a bit undergunned (not that they can handle any more weight on the stern) The one I used to go out on used to cruise at 16 or 19 knots which seemed slow for the hull to work properly.

How heavy are 90 etecs? I reckon two of those on a 5.2 would be ideal if they were light enough

[Dean1]

Ye my cruise is 23kts 4800rpm. I agree these hulls need to be at least say 21kts+ to work properly the faster the better in most cases. Cruise 16-19kts would be painfull in one of these.

90 etecs are still too heavy around 150kg each which is too heavy in my eyes.

A 90 hp 4 stroke weighing 120kg will rare its head in a few years i reckon the way technology is going but they wont be cheap.

[Out_There]

G'day, Very interesting thread guys. Just some numbers from a set up thats at the other end of the spectrum. Mines got two stroke yammie 90's (129 kgs), 340 ltrs fuel, largish clears and 2/3 on board dose 20kts at 3700 rpm, 25kts 4250rpm, wot is 37kts and 5600 rpm. Can't remember prop numbers, but std yammie.

[Dean1]

G'day, Very interesting thread guys. Just some numbers from a set up thats at the other end of the spectrum. Mines got two stroke yammie 90's (129 kgs), 340 ltrs fuel, largish clears and 2/3 on board dose 20kts at 3700 rpm, 25kts 4250rpm, wot is 37kts and 5600 rpm. Can't remember prop numbers, but std yammie.

Nice numbers Out There. Those numbers with 4 stroke fuel consumption would be ideal. You say 340 litres of fuel??? Have you had bigger tanks installed???

[Out_There]

Dean, Was told they were 180 ltr x 2 tanks, but reckon closer to 170. If I could repower, I'd be looking at suzuki 75's. Envious of the fuel burn of the 60's but don't like the idea of running an engine at 4800-5000 rpm continualy. Looked at tyhatsu? HPDI 90's a while ago but stuck with the yammies as i'd get nothing for them and they are a good donk.

[Danf]

Unsure about Chris's setup but normal practice is the controls trim both motors at the same time by pushing the one trim switch and the trim switches (binnacle switches) on the dash allow you to trim each motor seperatly. Thats how mine is set up and this is the correct way otherwise they would been a real pain to operate.

Deano.

So the trim set up with the new Suzukis is the same as the factory setup with the 2 stroke yamahas. You do need individual motor trim control as well as a common up/down switch.

[myusernam]

i would be very unhappy having a cruise at such high rpm.
22 knots at 4800 rpm (what the other guys are getting) is the go


As an aside have always thought the 5.2 kevlacats were a bit undergunned (not that they can handle any more weight on the stern) The one I used to go out on used to cruise at 16 or 19 knots which seemed slow for the hull to work properly.

How heavy are 90 etecs? I reckon two of those on a 5.2 would be ideal if they were light enough

WHOPS! typo I meat 18 or 19 knots. still too slow for a cat.

[OPTI]

any cruise rpm above 4200 is just crazy imop.seems like a tricky boat to power ,needs at least twin 90 hp,with no more than 110kg per side.

[Dean1]

Dean, Was told they were 180 ltr x 2 tanks, but reckon closer to 170. If I could repower, I'd be looking at suzuki 75's. Envious of the fuel burn of the 60's but don't like the idea of running an engine at 4800-5000 rpm continualy. Looked at tyhatsu? HPDI 90's a while ago but stuck with the yammies as i'd get nothing for them and they are a good donk.

Gee they are big tanks i wonder if they were installed from new?? Yours is a Black Marlin isn't it? What year is your hull? Mine is a Black Marlin a 1997 model maybe i have bigger tanks than i realize as these were the last ot the older 5.2's to be made.

Yes the 90 stroke Yammy is a good motor they would push your hull very nicely.

Cheers.

[Danf]

WHOPS! typo I meat 18 or 19 knots. still too slow for a cat.

I found the hull had to do at least 22 knots to achieve the better lift and ride.

[myusernam]

I found the hull had to do at least 22 knots to achieve the better lift and ride.

which then begs the question why does everyone rate them so much? dont get me wrong, when I went for few trips in one I thought it was a nicely finished boat (gamefisher model 5,2 when they first came out) did several hundered miles on a week long trip but just thought the performance was lacking....Didn't seem as though it couldn't handle heavier outboard though... they were two strokes and it was a long time ago

4800 rpm for 22 knots bites the big one. the poorest I would settle with. and I bet that is in calm conditions with no headwind or chop.

If I was buying I would seriously look at a pod extension to increase stern bouyancy and pit on bigger donks.

[Noelm]

The binnacle control on a Suzuki setup is a pretty simple thing, there is a rocker switch on the control that allows both motors together, or each by themselves, (as well as switches on the motors of course) there is no need for console/dash mounted separate trim switches, I never (well almost never) use the "together" setup, just use each motor switch on the control levers.

[Danf]

The binnacle control on a Suzuki setup is a pretty simple thing, there is a rocker switch on the control that allows both motors together, or each by themselves, (as well as switches on the motors of course) there is no need for console/dash mounted separate trim switches, I never (well almost never) use the "together" setup, just use each motor switch on the control levers.

Thanks for that. Now I have an idea how the tilt/trim is set up. Just wondering if you have any pictures of the dash set up that you can post.