Prop on 175 Sea Chaser

wellsc1 · May 3, 2009

I read quite a few prop post and got motivated to ask this. This Carolina Skiff has Yamaha 90 hp, 3-cyl., 2-cycle o/b with 13-1/4" x 17 stock aluminum prop. I tried same size prop in Mich. Wh. Rapture. WOT dropped from 5500 down to 4500 rpm, but speed increase about 7 mph (up to about 42 mph) and almost could not climb out on plane (max. rpm 3000 getting out of hole). I took the prop back and got a Yamaha ss black prop, 13 x 17 K. Haven't had moment to try it yet. Should I stay with the Yammy ss prop or consider other props that are cupped and with a full lobe for other boat performance?

junior1113 · May 3, 2009

Re: Prop on 175 Sea Chaser

i woud try a 19 with no cup cup is like another 1.5 in pitch bet you pick up a some speed and be in within wot #'s

hwsiii · May 3, 2009

Re: Prop on 175 Sea Chaser

Wellsc1, you are showing a Slip factor of 21% which is double what you should be showing for a boat that light. If that prop is not all nicked up then you are running too much diameter for your boat and wasting torque and horsepower that could be used for speed. The Rapture prop has way too much surface area and geometry for that combination. The Yamaha painted steel is a semi cleaver prop with very little surface area, you may be able to go to the 19" pitch in that prop, but try the 17" first, since you already have it. THe 17" painted steel ought to get you to about 40 MPH with very good RPM.

H

wellsc1 · May 4, 2009

Re: Prop on 175 Sea Chaser

Thank you both. I'll give the 17 pitch a try first. If wot goes over 5500 rpm, I'll be tempted to look up a 19 pitch with same cleaver design.

This is a great place to post!

Thanks...carl

hwsiii · May 4, 2009

Re: Prop on 175 Sea Chaser

You are very welcome Carl.

H

hwsiii · May 5, 2009

Re: Prop on 175 Sea Chaser

Carl, please update us with your test results as I use them in my database.

H

wellsc1 · May 6, 2009

Re: Prop on 175 Sea Chaser

I plan to go fishing around 1st weekend or so in June. Look for results posted shortly after that.

wellsc1 · Sep 8, 2009

Re: Prop on 175 Sea Chaser

hwsii,

I finally got on the water to fish over Labor Day weekend. The ss Yammy 13.25 x 17 black-painted prop did a little better than the Rapture with the hole shot, but it limited me to 3000 rpms until it climbed out of the hole. Top speed after playing with trim/tilt was 36 mph at 5100 rpm. At 4000 rpm, it did around 30 mph. I was able to trim up the motor more, much more than with the original aluminum. It seems my mpg was a bit less also. I had the motor checked out about 9 mos. ago.

Should I begin suspecting motor tune up or step down a pitch or two with a different ss prop? The place I bought the Rapture offered to exchange it for a 15 pitch full bladed prop.

For know, I put the alum prop back on to get my hole shot back and full rpm (5500) at sacrafice of a little speed.

hwsiii · Sep 8, 2009

Re: Prop on 175 Sea Chaser

Carl, you need to move the motor up at least one more notch on the transom and there is a good possibility it could be raised 2 notches. The semi Cleavers like to be high on the transom and perform best there just as most SS props do, they will give more RPM and speed higher on the transom. If you could get us a picture of the anti ventilation plate and the keel from the side and the back it will help.

H

wellsc1 · Sep 8, 2009

Re: Prop on 175 Sea Chaser

hwsii,

I'll get pictures soon.

BTW, regarding excessive slip with the aluminum prop... It had a couple slightly bent lobes from bumping a stump. I straightened them up to no noticeable difference with the known good lobe. Since I'm aiming for ss prop, I consider the aluminum prop temporary at this point.

Thanks for hanging in there with me.

wellsc1 · Oct 18, 2009

Re: Prop on 175 Sea Chaser

hwsiii said:
"...get us a picture of the anti ventilation plate and the keel from the side and the back..."

H

hwsiii, Finally, attached are some pictures. I think you'll see the anti ventilation place is approximately 2 inches above the absolute bottom point of the keel. I can go up a couple notches or down a notch. See that pic. also.

tnx...wellscw

junior1113 · Oct 18, 2009

Re: Prop on 175 Sea Chaser

seeing you have a pad. with what i can see i'd go up one hole and see if it helps or hurts. looks low too me.

wellsc1 · Oct 21, 2009

Re: Prop on 175 Sea Chaser

I found this on the Yamaha site. It's the exact match to my rig. I achieve practically the same results as presented on their "mph" chart for stated rpm. See the chart at the hotlink below. It's when I go to the recommeneded ss yamaha prop that the engines struggles to plane, dogging at 3000 rpms for a bit longer.

http://www.yamaha-motor.com/assets/...okePerf_HPMidPort_90hp_CSK-SC175RG-90TLRB.pdf

Do I still need to raise the engine or run through fuel system?

wellsc1 · Dec 1, 2009

Re: Prop on 175 Sea Chaser

hwsiii said:
Wellsc1, you are showing a Slip factor of 21% which is double what you should be showing for a boat that light. If that prop is not all nicked up then you are running too much diameter for your boat and wasting torque and horsepower that could be used for speed. The Rapture prop has way too much surface area and geometry for that combination. The Yamaha painted steel is a semi cleaver prop with very little surface area, you may be able to go to the 19" pitch in that prop, but try the 17" first, since you already have it. THe 17" painted steel ought to get you to about 40 MPH with very good RPM.

H

HWSII,

This won't be scientific. I think the Yammy black ss prop is working now, actually the 90 hp 2-cyc. o/b. I got a chance to try it out again on recent fishing trip after changing the spin-on fuel filter and cleaning the motor's inline filter. The motor was still sluggish getting out of the hole, but it came out well enough to keep the prop on all 4 days fishing. WOT was 5100 to 5200 rpm at 37 mph (per GPS). I suspect restricted filter from bad gas that may have been in the boat when I bought is used and it's finally diluted enough from a few trips fishing to have little affect now. In any event, I will have the carbs cleaned and re-tune engine now. I might make 40 mph and 5500 WOT yet. I will still post performance stats later.

Yes, the aluminum prop has some light nicks in it. First time out, I bumped a stump at idle speed and bent two of the lobes. I hammered them back in place, but felt guilty doing it. Now that it is destined to become a spare prop, I may just leave it in the "guilty" condition. Anyone with an opinion about my guilty plea, please help me exonerate myself on what to do about the spare prop.

hwsiii · Dec 3, 2009

Re: Prop on 175 Sea Chaser

carl, I would move the motor up one more notch at least, that semi cleaver prop NEEDS to run HIGH in the water column for its maximum performance. It will increase the RPM and the maximum speed. Your aluminum prop was not ventilating at the height you have it now, so that tells me you need to go higher. In the prop test that Yamaha used it was only an aluminum prop, not a stainless steel higher performance prop.

You might try reading this for a better understanding of changing props for better performance.

http://forums.iboats.com/showthread.php?t=365653

H

wellsc1 · Dec 3, 2009

Re: Prop on 175 Sea Chaser

hwsii

Thanks. Currently the ventilation plate is at or just above the keel, but the keel is a bit recessed under the transom as the picture may be clear enough to see. If I raise the motor up a notch, will the invite water thrown up at the transom?

Right now, I have the boat at the mechanic for carb. work (suspected clogged low speed jet on one cylinder) and basic tune up overall. Once I get it back, I have hopes it will have a better hole shot.

Moving the motor is a bit intimidating for this shade tree mechanic, but not scary. I hope the lift points are on the motor. 3M 5200 is what I use on the bolts, correct?

Dhadley · Dec 3, 2009

Re: Prop on 175 Sea Chaser

The motor is about as low as you want to have it. It'd be much better a little higher but maybe not with that particular prop.

Lower will invite water up the transom, going higher will not.

Use 5200 on the bolts only if you never want to remove them or move the motor again.

That's a decent looking hull design. It'd be worth it to look at a prop with a little more technology.

wellsc1 · Jun 8, 2010

Re: Prop on 175 Sea Chaser

hwsii,

You were "spot on" with "THe 17" painted steel ought to get you to about 40 MPH with very good RPM."

After a carb clean, which found the low-speed jets dirty/restricted, the boat all but jumps out of the hole. I still want to record stats of performance and post to this thread. For now, it is doing 39 mph at 5200 rpm without much spending a lot of time tweaking trim/tilt and max throttle. That includes a full load of fuel (25 gals.), fishing tackle and bait, back-seat ice chest full of drinks and ice, front ice chest half full of ice for fish, the wife, and the dog. I may be missing a few items, but not the wife and dog. Oh yeah, me driving the boat.

There is no water spraying up the transom. If I raised the motor up a notch, I'm "afeared" my sharp cornering at higher speeds may ventilate the prop like my brother-in-law's boat does. In one part of the river with a bunch of sharp turns, he has to go just above planing speed to keep his prop biting, which causes me to rumble along behind him at around 3800 rpm. He's got an aluminum prop still.

Anyway, back to my ss Yammy prop. I'm happy with it, now that my motor has happy carbs and a clean fuel system.

Prop on 175 Sea Chaser

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