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Author Topic:   Gear Ratio for 1981 235 Johnson
caddis posted 07-23-2001 04:47 PM ET (US)   Profile for caddis   Send Email to caddis  
It was determined at the Rendezvous this weekend that I am way underpropped. According to my guru lhg, I need to know the gear ratio of my motor to determine which pitch I need. Does anyone here have this info? Or does anyone else have a prop recommendation for my 1981 Revenge V-22?
Bigshot posted 07-23-2001 07:58 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Brochure says 14:26 (.54) whatever that means. What are you running now as in prop and WOT rpm's?
caddis posted 07-23-2001 08:13 PM ET (US)     Profile for caddis  Send Email to caddis     
I should probably have called it gear reduction. Right now I have a 15X17 prop. Previous owner was a troller with downriggers and outriggers, so it worked for him. RPM's are through the roof- at least 6,000, but have not ventured beyond that, quickly reducing from there. Motor was recently rebuilt, so I'm not used to it yet.
lhg posted 07-24-2001 12:23 AM ET (US)     Profile for lhg    
Todd - You sure didn't waste much time getting this posted.

If Bigshot's # of gear teeth are correct, your engine has a 1.86:1 gear reduction, which is the same as the 200HP Mercury.

Also assuming your older 235 Johnson will run about the same as a 200 HP Merc, Mercury's prop charts are showing a 19" pitch prop, load capacity of 2600-4500lb, speed range of 44-51 MPH. This sounds about right to me. I would say your boat should be capable of doing 46-48mph.

They also show a 17" pitch prop, load capacity of 2900-5000, speed range of 38-46MPH. This could work also, especially with a heavily loaded boat, when that 100lb pooch is aboard!

Above numbers are at 5600 rpm max.

Either way, something is wrong with your current prop. It seems to have lost it's pitch. Since you only need a temporary solution, you might consider having it repaired, and re-pitched to 18" or so.

You should really be running an SS prop on a boat like yours. Once you get above 30mph, that alone would be worth 2 mph.

Bigshot posted 07-24-2001 09:52 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Ditto! I think the 19 will work great, especially SS. Your tach might be off too, but you will find out. If the 19 is still reving on the high side, you can double cup it and bring down the r's. Start with a 19"
lhg posted 07-24-2001 02:53 PM ET (US)     Profile for lhg    
With a fresh nights sleep, the only other thing I should add here is the HP output of your engine. I have no experience with a 20 yr old 235HP OMC, but it's possible that, in spite of the rebuild, its not as strong as new Merc 200, for which I was using the prop charts. So some caution should be exercised there in prop selection.
caddis posted 07-24-2001 03:26 PM ET (US)     Profile for caddis  Send Email to caddis     

Welcome back! I'm sure you were as anxious to leave as we were (hint of sarcasm).

Following your advice, I picked up a 14 1/2X19 Michigan Wheel prop. I just couldn't pop for the stainless since the motor is only temporary. Bummer, since I have two brand new Yamaha 13X19 stainless props just sitting in my office at home.

You also recommended a 17" pitch, but that is what I (supposedly) have on right now. I don't think that will be the way for me to go. I can always reuse (and rebuild) that one, though.


Thanks for the numbers. Without those I would have been doing way too much guesswork.

I'll put the new one on and drop her in tonight. I will post the results here.

Bigshot posted 07-24-2001 03:28 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
lhg posted 07-24-2001 04:53 PM ET (US)     Profile for lhg    
One final thought - the rubber hub in your old prop could be letting go at higher RPM.
Don't even know if OMC props have the rubber hub like the Mercs do, but if so, that could also be your problem.

I've got to say, that prop you were running was a "beater"! Also, someone could have had the prop re-pitched lower. Never really know about something like that. A new prop was the right choice.

(for others reading this, caddis has a really nice 1981 22' Revenge).

caddis posted 07-25-2001 11:44 AM ET (US)     Profile for caddis  Send Email to caddis     
Okay, it's back to the drawing board.

Although the weather was less than cooperative, I still am not getting the predicted performance here. I put the new prop on and took her up to WOT. Mostly got a reading on the gps of 37 mph, with a possible top reading of 40 mph (we never actually saw it hit that speed, it just registered as the top speed). However, the tach at times was all over the place. When I first started the engine I had to give it a little gas in neutral, and the tach just stuck at 3000 rpm for a few minutes even though I backed her off to idle. Was that normal? There were times it seemed it was reading way too high. Once I thought it stabilized, it looked like WOT was about 5200 rpm. Neutral was registering around 1100 rpm, but it sure didn't sound like it. Now I don't trust it and will have to try a new one to see if it was accurate.

Another possibility. LHG, you might remember when we were working on my throttle cable I said that after the rebuild they had set the throttle with more forward thrust than reverse. It could be that at WOT I just don't have enough room to push the lever down further unless I adjust the neutral back to the way they had it, which would take away from my reverse power (look out for the dock!) Could this mean there is too much cable and an adjustment at the motor is necessary?

Also, you had mentioned that the carbs may need adjusting. Should I try that? I plan on putting in new plugs, since the ones that are in there had to operate with the overly rich mixture from the first hours after the rebuild and could be fouled. I'll also run a compression check just to be sure that the guys at the shop did their job.

Any other suggestions?


Bigshot posted 07-25-2001 01:02 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Let the shop readjust everything including your throttle cable. You have 2 cables, throttle and shift, The shift is the one affecting your FNR and as long as that works good leave it alone. The throttle cable is easy to tell. Is it hitting full throttle? Look at carbs and see if they are pegged. Engine should be off when doing this.

Did you change your voltage regulator or rectifier(silver round thing? If so then your tach sounds screwy and being 20 years old it might. I had a 79 115 merc that we fiddled with everything because it was only getting 4500. It idled right, etc. Then i replaced tach for S&G and it went to 5300.

LarrySherman posted 09-23-2001 12:33 AM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     

What was the result of your prop experiment? I'm in the midts of the same quandry with a 1985 235 on a 25. Would love to benifit from your firsthand experience.

Thanks, Larry

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