Correct WOT

[ken52]

I've been tring to find in my clymer manual(worst manual ever owned) what my wot should be but cannot find it. I have a 87 Pro-Line 21 WAC w/ 1987 Evinrude 140 looper motor. I guess the boat, motor,fuel, etc gives me a weight of about 3500-4000 pounds. I have a 13 3/4 x 15 alluminum prop and I am getting 5100 rpm with about 28 knots (gps) at wot. Is that about right for this setup? Any help or suggestions is greatly appreciated.

Ken

 

[tashasdaddy]

Re: Correct WOT

rather see 5500-6000, due to todays fuel. it will run cooler and better. according to the original specs, 4500-5500, so it is up to you if you want to change props. but before changing, besure you motor is properly tuned. if you have not done a decarb, i suggest one.

 

[ken52]

Re: Correct WOT

Tashasdaddy,
Boat has just be tuned up and all carbs cleaned and adjusted. Run and idles very good. I assume when you say decarb you mean to clean the carbon off pistons? I remember reading something about spraying something into plug holes to clean that up but I have never done one yet. To bring up the rpm's if I am correct I need to go down in pitch say like from 15 to 13, is that correct?

Ken

 

[HighTrim]

Re: Correct WOT

I agree with TD, your WOT RPMS are much too low. I would aim for more of 5800 RPM. You are correct, decreasing the pitch will increase the RPMS. I would also check the spark first just to ensure you are firing on all cylinders before buying a new prop. What is your current set up? Positive you have not taken on water correct?

As far as a decarb goes, check out the FAQ or do a search, you will find plenty of reading material on it. A tried and tested product for this is Seafoam, you can pick it up at any NAPA store or the like.

 

[ken52]

Re: Correct WOT

Chris,
Not sure exactly what you mean by current setup, but it's a 1987 Pro-Line 21 WAC with an 1987 Evinrude 140 looper motor, 13 3/4 x 15 3 blade alluminum prop(not sure mfg) and a 7.5hp Merc kicker. Motor has just been tuned up, carbs removed and cleaned with correct jets. It idles at about 1K and drop to about 800 when in gear. It jumps on plane very nice with myself and 70gl of fuel and a few things. I do have a little bypass comming from 1 spark plug due to someone prior to me sleeving the threads, my be loosing some there but wouldn't think 800 rpm's.

Ken

 

[wilde1j]

Re: Correct WOT

Before trying a new prop, make sure motor is not rigged too deep. If water covers the cav plate @ WOT, it's too deep. Come up a hole at a time, watching for cavitation in tight fast turns. Cav plate should be uncovered when you have it right. RPM's will come up as part of this process. If RPM's are still too low, it's time to mess with props.

 

[ezeke]

Re: Correct WOT

If my math is correct, that's over 20% slip on your current prop. I would experiment with the trim a bit to try to keep the A/V plate level with the water at WOT, then do as wilde1j suggests and see if raising the motor a bit doesn't improve things.

If the boat in fact is rated for 200HP, the 140HP motor is the threshold, so you may have to resort to a lower pitch prop to keep from lugging the engine.

 

[ken52]

Re: Correct WOT

Jim & Ezeki,
Thanks for responses. My AV plate set just about 1/2" below transom, so it appears it is rigged ok. My choices of prop change are a 13 3/4x13 3 blade or 13 1/4x13 4 blade. I thought maybe the 4 blade would be better and it might let me back off on the rpm's at a lower speed before she squats down in the water. Right now I have to keep it at about 3800 rpm to keep on plane. Any thoughts on my blade choices? Is it ok to drop down to a 13 1/4" blade from the 13 3/4" ?

 

[wilde1j]

Re: Correct WOT

If the plate is 1/2" BELOW the hull bottom, it's probably NOT OK. Also, is is covered or not @ WOT?

 

[ken52]

Re: Correct WOT

Don't know if AV is above water at wot. Will have to check it the next time out and I have someone with me. I'm assuming it should be riding above the water at wot?

 

[wilde1j]

Re: Correct WOT

It should not be covered with water when boat is properly trimmed.

 

[ken52]

Re: Correct WOT

After checking boat again, I place a 3' yard stick flat on hull center ridge and with the motor fully trimmed down the leading edge of AV plate is about 1" below and trailing edge drops even further. So it does look like I habe to raise motor. Now I have a tractor with a bucket that I can lift with but not sure where on motor to lift from without damaging motor. I thought I read at one time there is a lifting ring that attaches to flywheel. Could you use webbed strping to lift motor with without hurting anything or how could I do this?

 

[wilde1j]

Re: Correct WOT

Whoa big fella. Do you have a trailer for the boat? There's a way easy way if you do.

 

[ken52]

Re: Correct WOT

Yes, boat is sitting on trailer, I haul it back and forth to the water.

 

[wilde1j]

Re: Correct WOT

The whole deal takes 20 minutes (for two motors) and NO lifting requied. Make sure the trailer is on a level, hard surface, block one side wheels, block a skeg with the motor down, loosen the lower bolts, remove the uppers and start cranking the tongue jack (trailer not connected to tow vehicle of course) till you're lined up with the hole set you want. Replace upper bolts, tighten lower and uppers .... done! Procedure works with all outboards I know of. A little more trouble if someone slathered 5200 sealant all over.

 

[ken52]

Re: Correct WOT

When you say block skeg, do you mean to put some wood supports under skeg so it doesn't dig into ground or should I place wood supports on both sides of skeg to bottom of AV plate for support ?

 

[wilde1j]

Re: Correct WOT

When you say block skeg, do you mean to put some wood supports under skeg so it doesn't dig into ground or should I place wood supports on both sides of skeg to bottom of AV plate for support ?

Wood under skeg. The idea is to keep skeg form burying itself in pavement and also to minimize the cranking at the front of the trailer. Do NOT put load on AV plate (it will break).

 

[ken52]

Re: Correct WOT

Thanks Jim. Will do that and see what changes in rpm's, than will decide on re-proping motor. Of course will have to wait for water test here in FL due to all this rain and choppy water!

 

[ken52]

Re: Correct WOT

Well moved motor to the top hole from thr bottom hole. Today I went for a water test . Was able to achieve almost 6000 rpms on the 13 3/4 x15 prop, but the more I trimmed up to gain the increase in rpm's my speed went down and when I went into a hard turn I motor over rpm & lost bite on the prop. I guess it must be comming out of the water to much. The best I got at wot was about 5200 rpm @ 31 mph(gps spped). The motor actually sounded beter though when it was deeper in the water, when I had it trimmed up it sounded like there was more strain on the motor. I going to try moving motor down to center hole and see if that has a better bite on water in hard turns so I don't have to back off the trottle to keep prop lower in water. Just a little confused here, I thought I would get better performance when the motor was running up near the 6K rpm range or am I missing or doing something wrong?

 

[wilde1j]

Re: Correct WOT

If you get too high you lose speed. Move one hole at a time and check to see if the AV plate is covered or not. Also, trim for max speed (using GPS). Also, if the motor cavitates in turns, it's too high. This is totally done by experimenting.