Repowered 5.2 KC with twin 60 suzuki's.

[Chris20984]

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.

[finding_time]

Chris

I've got 15's on my yami's, i ran them as is for around 600hrs until one day at the ramp i had a slight mishap and damaged both props so whilst they were being repaired i had them reshaped to give me more RPM as i only used to be able to get 5600- 5700 out of both engines and this is just below spec for the motors. After getting them reduced a fraction i now get 6000 rpm but have lost about 1.5 knots top speed but have noticably more pick up! I think i'll get more engine (gear box) life out of the engines now there working properly and this was the reason i did the modification!

I have never subscribed to the notion that you need hull shot for bar work it's pure B/S imho! And i'll back this up by saying the supposed guru of Bar crossing work down this way is Bill Corten and he changed his 225 hpdi over for 150 hpdi on a 625 cruisecraft , if hull shot was that important he would have the bigger engine on as that's a heavy rig with 5 people on board!

Sandy Cape / Breaksea is a little unique in that if the inner 2 mile 4 mile and 8 mile are on the iffy side you can alway travel down to the 13 mile and cross at will so why would you risk the closer crossings on a bad day? the better fishing is around the 13 mile crossiing anyway!

ian

[Lovey80]

I recon definitely try the 15's. Those suzuki gearboxes tend to be able to throw a slightly bigger prop that their rivals. You will probably find that you'll increase your fuel economy and top end speed with very little drop in punch or revs (your at the top of the rev range now I would imagine). With 3 blokes on board I think you can afford to drop some revs anyhow.

[Dean1]

Congrats on the new donks Chris they look shithot! Ive always liked black outboards Their good numbers your getting there and would be very suitable but try the 15's youll know straight away if you like them. 14's on my yammies were terrible my top speed was 24kts at 6000rpm.

Id say the turbulence problem is no spray plates they are a must on these boats. Mine never digs its arse down. I keep them trimmed in till i get on plane then trim out and it lifts out of the water.

Let us know how the 15's go im keen to hear the outcome.
Good luck enjoy.

Deano.

[OPTI]

try a set of 4 blade;s

[Noelm]

It might be worth paying the money and getting Solas to come out and try a range of props to get maximum benefit. Pretty good motors the 60 Suzuki hey! very light, nice sound and great fuel economy.

[julian1]

yep i agree try the 15's if theyre still not quite right call Solas, i'm not sure they do a little 4 blade for them yet ?

yes a grunty little 60 the new Zuke, from a few comparo's ive seen they out perform the Yam 60 and very close to the Yam 70 apparently

[Noelm]

yep, I reckon you would be right there, they are a nice engine, have you noticed how soft the engine mounts are on the Suzukies? kind of scares me a bit, they are so springy, compared to (say) a Merc or other brand, after the 90HP they are reasonably hard though.

[PB]

How do the 4 blade props go in reverse on a cat?
most mono's Ive been on are not all that good in reverse.
I was talking to a guy on the weekend that had put 4 blade props on a 27 Noosa Cat and it was hopeless, ended up putting the 3 blade props back on.

[Noelm]

well I guess all things are a compromise, most tend not to travel too far in reverse, so if there is an advantage in lifting the stern, and better performance, I reckon i would put up with bad reverse problem.

[julian1]

How do the 4 blade props go in reverse on a cat?
most mono's Ive been on are not all that good in reverse.
I was talking to a guy on the weekend that had put 4 blade props on a 27 Noosa Cat and it was hopeless, ended up putting the 3 blade props back on.

that seems odd Daniel, do you mean how does the boat go backwards ? the 2700 needs all of the rear end lift it can get and 4 bladers help a lot as i have on mine, it rides and performs heaps better, no drama's in reverse either.

what engines is he running ?

[PB]

Yeah I thought so to Julian, I was talking to Tim from Invy about it, it would have been Yamaha but not sure what size. he said that they couldn't even back the boat of the trailer went back to the 3 blade prop and problem solved.
I went out in a 5.8m plate mono similar to one of mine but different brand fitted with a 150 opti and a 4 bladder, and it was hopeless in reverse but awesome going forwards (had nothing to do with the boat design).

Yes it's true you don't use reverse a lot but when you need to pull up in a hurry say at a jetty or loading on the trailer you want it work.

[julian1]

strange i have never ever noticed a problem on my last two cats with the 4 bladers ??

[Camhawk88]

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



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

Cheers Chris.

WOT at 6300 sounds a bit excessive to me- suprised no one has mentioned it. Perhaps it is ok for this motor but I was always of the opinion that a correctly proped 4 stroke would rev between 5800 and 6000 at WOT. I would also expect a cruise speed in the low 20s and at revs of around 4200.
I would be inclined to at least try out a 15" pitch and would imagine you might improve your top end a bit, I would have thought a 5.2 Kevcat with twin 60s should be able to achieve closer to 35kn. Doubt there would be any noticeable decline in holeshot with a 15- only one way to find out.
Also- not sure if it just the photos, but the motors seem to be very low. does the cav plate draw about level with the bottom of the hull? They look to be well below which may hinder your performance, as I said, could just be the angle of the photo.

Cheers,

[julian1]

WOT at 6300 sounds a bit excessive to me- suprised no one has mentioned it. Perhaps it is ok for this motor but I was always of the opinion that a correctly proped 4 stroke would rev between 5800 and 6000 at WOT. I would also expect a cruise speed in the low 20s and at revs of around 4200.
I would be inclined to at least try out a 15" pitch and would imagine you might improve your top end a bit, I would have thought a 5.2 Kevcat with twin 60s should be able to achieve closer to 35kn. Doubt there would be any noticeable decline in holeshot with a 15- only one way to find out.
Also- not sure if it just the photos, but the motors seem to be very low. does the cav plate draw about level with the bottom of the hull? They look to be well below which may hinder your performance, as I said, could just be the angle of the photo.

Cheers,

yes exactly, you will be better off getting your engine height spot on before exchanging props, there will be some experienced with KC5.2's on here but i bet you will almost get away with having the cav plates level with the bottom of the pods. you should be getting a nice clean wake at planning speeds with minimal sprinkler water coming off the engines, or walk down the back and see where your cav plates are sitting while on the plane. if you are hitting 6300rpm with fuel and 3 blokes and your engines are too low then you will find that it will spin the next pitch prop easily and maybe even more, by the way you described the handling the enginesare probably too low, you will be surpirsed by how much difference it can make.