Prop Kencraft 180 Challenger with F100

[keada714]

Hey guys,

Currently I own a kencraft 180 challenger which is pushed with a yamaha f100 with hydrofoil. The current yamaha alum 13.5x15k propeller has a couple little dings from hitting the anode trim tab. I would like to replace it with another prop however, I believe the engine is over proped. The manual calls out for a WOT range of 5000-6000RPM, however, I cannot get the engine to turn at the higher range.

The engine revs up to 5200 at wot with 1/4 of fuel (10 gallons), 3 guys and 10 hoop nets. This is usually the load that I will have on the boat minus the hoop nets plus more fuel. The motor is mounted at the highest position and does not porpoise and the anti cavitation plates looks to be above the water flow when i'm at WOT. So I was wondering if you guys can give me some reccomendation on what kind of prop should I be looking to purcahse. SS vs alum, 4 vs 3blade, brands and of course at what pitch. Any feedback would be greatly appericated! Thanks

 

[steelespike]

Re: Prop Kencraft 180 Challenger with F100

We need your wot rpm and "speed" hopefully by gps. Assuming a 2.31 gear ratio 5200 rpm would produce about 28 mph guessing 12% slip.Unfortunately the 100 doesn't have any test reports to check out.
Couldn't even get it to come up on the Yamaha site. There is no doubt that if the foil is in the water it can create drag both from the foil and the hull attitude.The 15" seems like a reasonable size. I think I read somewhere that Solace makes Yamaha props.
Before A prop change I'd like to see the results with no foil.Don't worry about holes being left.

 

[keada714]

Re: Prop Kencraft 180 Challenger with F100

Got some more time on the water today. This time by myself with a qtr tank. Got it up to 5500 and my plotter/FF says i was doing 31mph. So it looks like I am getting roughly 9 percent slip. Going to remove the foil on my next outing and report back.

Quick questions though, if I decided to pick up a alum propwith 3 blade and 13 pitch, would I see any improvement in top speed and efficiency?

 

[steelespike]

Re: Prop Kencraft 180 Challenger with F100

Couldn't find any F100 info but going to a 13" prop should add 300-400 rpm assuming 9% slip and 5900 rpm speed would be about 28.
Hole shot would probably be amazing. Speed should hold up well when adding weight.

 

[keada714]

Re: Prop Kencraft 180 Challenger with F100

Took it out again, this time with two buddies and half a tank of gas. No increase in RPM with the hydrofil off. Did noticed it took longer to get onto plane and there was a more bow lift. So i put the hydrolfoil back on. THen had my friend take her up to WOT while i looked at the anti-cavitation plate. Plate/hydrolfoil looks to be under water..

So I went home and did a quick measurement. The anit-cavitation plate is about half an inch higher than the lowest part of the boat. The motor is already mounted on the lowest hole, in turns, lifts the engine at the highest position. Would my only option be buying jack plates?? Did not want to go this route as they can be quite expensive. Any other suggestion on raising it without spending a fortune?

 

[keada714]

Re: Prop Kencraft 180 Challenger with F100

Bump... Any suggestions??

 

[jestor68]

Re: Prop Kencraft 180 Challenger with F100

Your Yamaha owner manual will tell you that your motor is rated at 100 hp @ 5500 rpm, which a range of 5K-6K rpm.

So realistically, your rpm range is 5500-6000 rpm.

It has a 2.15 gear ratio.

I suspect your F100 is down on power compared to a new motor. Therefore the motor is telling you what it needs.

If it can just muster 5500 rpm with a light load, it's likely that you need to reduce pitch to a 13 to get the rpm up closer to 5800-5900 lightly loaded. That way when you carry your usual load, it should still be able to muster 5500+ rpm.

The prop should not be hitting the anode fin if it's the correct prop for the motor.

 

[keada714]

Re: Prop Kencraft 180 Challenger with F100

Thanks for the response jestor. I will invest in getting proped correctly once I raise the motor more. However, I am very limited in what I would need to do to raise the motor as it is already raise at its highest.

What would my best option be to raise it up? I was looking at static vertical jack plate. As I don't want to spend to much money nor do I want the outboard to be set back any.. Any information regarding this would be greatly appreciated!

 

[steelespike]

Re: Prop Kencraft 180 Challenger with F100

Set back is usually a good thing though it might require more height.If the mount bracket is is on the top of the transom you may be able to simply raise the bracket.I've seen them as much as about 2" higher than the transom.
It's possible you may have to raise it an inch or so and lower it a half a hole on the bracket.
At this point I wonder if a slight raising of the motor will result in any real improvement.
What is the hp rating of the boat? Is it considered a fast hull?is it a Deep V?
Have you confirmed that the motor is in excellent tune and is the throttle opening all the way?
I have to agree with Jestor I think you may be down on power.
I see 90 hp tests pushing 1500 lb boats close to 40 mph. While I think the gear ratio is different
than 2.15 at 2.33 they are using props as high at 19" pitch.

 

[keada714]

Re: Prop Kencraft 180 Challenger with F100

Steel,

I do not follow what your saying in regards to rasing the bracket. Thought the bracket is fixed on the outboard and the only real adjustment is to lift the outboard and mount together and remounte onto the transmon. In this case, is already at its fullest.

The maxium rating for the boat is 115HP. It is a deep-v ceter console that weighs about 1500 (dry of course). How could i confirm that the outboard is down on power.. I have not encoutner anything that tells me otherwise. Beside the information you are telling me in regards that there is similar boats pushing a 19" pitch and reacing 40mph.

Ran out to do a quick compression test on the cylinders. At WOT with the engine warmed up, all four cylinder reads 205 +-5 psi. I know the carbs are very sensitive and can be a PITA to sync, but it idles great and doesn't show any real signs of need anything. When i first took the boat out, i thought it would have a better hole shot as well as top end. It feels like the boat is over proped as it feel like the boat is being lugged around.

 

[steelespike]

Re: Prop Kencraft 180 Challenger with F100

Most larger motors have a height adjustment in the mount bracket itself.Usually the bracket is attached so the lip rests on the top
of the transom then height is adjusted within the bracelet assembly.
If the motor needs to be raised further usually the whole bracket can be raised and then the bracket adjustment is used.
Your compression is a good sign.
Being down on power could be as simple as the throttle cable adjusted wrong or defective.
Or something wrong with linkage under the cowl.
If it has a timing adjustment it may be set wrong. It probably has electronic timing advance but it wouldn't hurt to check
the timing.
You could check out the performance reports on the net.
look for Yamaha performance bulletin. Check the 90s They do have a different ratio but the key is the performance.
I did a very brief look earlier If I recall right the typical prop was a 17" I recall one speed of 37.
Also one prop at 19" These were all very brief checks I might have missed key details.
Boats I checked were all at least 1500 lbs.

 

[keada714]

Thanks for the help guys. You were right, it was down on its power. Cylinder 4 ran rich and cause the lack of power. Turn out to be carb number 4 was missing the pilot jet plug. Replaced it and the engine ran great! Spun 6100 rpm at 29 kts. Slip is about 12%, so I will just have to live with that!