Am I fast or slow?

[floyd fish5033]

I have a 1976 18' fiberglass with an omc i/o 190<br />in it. Out testing the boat I was hitting about 42mph. This is after cleaning the carb and other baisic maintaining. Is this about the expected range for this boat or should I expect more? (the prop is a 16).Thanks!

 

[Reel Poor]

Re: Am I fast or slow?

Really need more information. Hull design, engine RPMs. What kind of boat is it?<br />I would not expect it the be any faster. Just from your brief description I would have Guessed around 40. Maybe a little slower, 38.

 

[floyd fish5033]

Re: Am I fast or slow?

Thanks Reel, It's a 1976 Starfire V-hull.<br />omc 190 i/o sterndrive. I'm running about 5600 rpm at full throttle.

 

[QC]

Re: Am I fast or slow?

RPM is really high. My guess is tach is wrong, but you need to find out for sure. I beleive it should be from 4200 - 4600.

 

[Boatist]

Re: Am I fast or slow?

If your tach is right your engine is in danger from way to high RPMS. Again if your tack is right you would get a lot more speed and better fuel mileage from a 21 pitch prop and get your motor down to 4600 RPMS where it should be.

 

[floyd fish5033]

Re: Am I fast or slow?

I'm on my way to get a new prop.<br />21 or 18?

 

[Reel Poor]

Re: Am I fast or slow?

Before you get a new prop Make Sure Your Tach Is Accurate .<br /><br />What size and pitch prop are you running now?

 

[floyd fish5033]

Re: Am I fast or slow?

All I know is the boat shop here called it a 16. is this size or pitch and can it be found on the prop?

 

[Boatist]

Re: Am I fast or slow?

If your pitch is 16 and your tack in correct turning 5600 RPMS then you can go up to a 21 pitch of the same size.<br />Each 1 inch increase in pitch will make about a 200 RPM difference. So a prop of the same diameter and type should turn 200 RPM slower for each 1 inch increase in pitch.<br />16 = 5600<br />17 = 5400<br />18 = 5200<br />19 = 5000<br />20 = 4800<br />21 = 4600.<br />Since it is never exact only buy a prop from some one who will let you exchange the prop if it turn out to be wrong.<br /><br />Make sure your Tack is right. Very common for tack to be set wrong. Like instead of being set for a 6 cylinder it set to a 4 cylinder. Call the dealer you are going to buy your prop from. Tell them your RPM per your tack is 5600 RPMS but you would like to have tack checked before you buy a prop from them. I think they would likely check for very low on no cost to get your business. <br /><br />In general props eaiser to find in odd sizes like 17, 19, 21. If your tack is wrong and you up the pitch you can also damage your engine from lugging so get it checked first.

 

[floyd fish5033]

Re: Am I fast or slow?

Thanks Guys, outstanding info.<br />I'll let you know what I find out.

 

[Reel Poor]

Re: Am I fast or slow?

My money is on the tach being off.<br /><br />I just dont think the 190 is goin to turn a 21 pitch prop on that boat.

 

[cobra 3.0]

Re: Am I fast or slow?

That 190, is a 3.0 litre 4 cylinder engine? No way you can turn a 21" prop on an 18 foot boat. That should read 4600 not 5600 rpm. Everything else seems correct. Your speedometer may be showing a little high too. 40 mph is high for a 16" pitch...more like 35-37 mph if you check it with a GPS.

 

[ae708]

Re: Am I fast or slow?

I can easily run a 21" prop on my 18' boat with Mercruiser 3.0 130hp. My rpm's are down to around 4400 from 46ish with the 19. Acceleration is a bit slower, speed is the same as with the 19.... 42mph by GPS, 47 by speedometer.

 

[cobra 3.0]

Re: Am I fast or slow?

Yes in your case sure. This is a 1976 boat lacking the newer stepped hull design. I suppose until we really now actual rpm and speed verified by GPS, we really can't say what he needs.

 

[Northern Eclipse]

Re: Am I fast or slow?

A 190hp OMC from that vintage is not a 4 cyl it very well could be a ford 302 block or a 3.8 v6 21p will be the ticket if tach is correct. 16p seems to small for a 18ft with 190 ponies.

 

[cobra 3.0]

Re: Am I fast or slow?

190 hp or 190 cu in.? (3.0 is 188 cu in. I believe)

 

[Reel Poor]

Re: Am I fast or slow?

posted by Northern Eclipse <br /><br />it very well could be a ford 302 block

I just did a little checking on the 190hp.<br /><br />Northern Eclipse nailed it. <br /><br />Wellllll, it MIGHT turn a 21 now. <br /><br />I was thinking 4 cyl. <br /><br />I guess thats what I get for thinking huh??

 

[Boatist]

Re: Am I fast or slow?

I do not know about 1976 but in 1980 OMC's 185 HP was 305 cubic inch V8. The 200, 230, and 260 HP was 350 cubic inch V8. WOT on the 1980 185 HP is 4000-4400. WOT on the 1980 200 HP, 230HP AND 260HP was 4200-4600 RPMS.<br />The 3.0L 181 cubic inch is 140HP and WOT is 4200-4600 RPMS.