Is 90 hp adequate for 1967 19'6" bowrider?

[doughert0]

I have a 1967 seacraft bowrider, 19'6", 1150 lbs empty weight. I have been running 115 hp but the 2009 motors are 75 to 100 lbs heavier than my 1999 Johnson special, and have a much higher profile.

Seems like years ago folks were regularly running 90 hp engines on this hull. Anyone know whether a 90 would be adequate. I fish in salt water, and if I top out at 20 kts I'm happy - the 115 gives me about 25. Most times it's too rough to run that fast. I sometimes have four adults in the boat, and ususally start out with 42 gallons of gas. Normal operating weight would be about 2000-2200 lbs.

Any thoughts?

[McGillicuddy]

Hey Bowrider,
I think 90 is fine for that hull. Fr. Frank's running a 90 optimax (375 lbs) on a Seafari and I think he mentioned he can get 28 mph; and 4 or 5 mpg avg... 25 seems kind of low for a 115 on a Bowrider. Make sure your motor is set to the right height. Anti-cav plate should be about 1-1/2" above the keel. Sound's like your currently set too low or you're propped wrong.

What rpm do you get at WOT. And what prop are you using?

[Fr. Frank]

I have a '06 90 Optimax on an 1800 lb Seafari, and cruise at 25 mph, and top out at 33 mph (now that I've got it propped right). At cruise I get 5 mpg.

In the early 1980's I sold a number of new 20' SeaCrafts rigged with 85 and 90 hp Johnson V4's.

Finally, how much power is enough? Out in the Gulf of Mexico, even when I had 150+ hp on this same boat, I generally cruised at about 25 mph or so. Now I still cruise at 25 and use about 40% less fuel than before.

90 hp is enough, except for slalom skiiing.

[65Bowrider]

Welcome to the site!!!
I have a 1966 bowrider with 115hp ETEC & the boat performs very well ... 3 people, 3/4 tank fuel, WOT is 39mph.
A 90 should push her well with the proper set-up as Frank stated, but she also handles the weight of the ETEC 115 well too (370 lbs).
Original fuel tanks were 29 gals ... have you done some modifications?
Any pictures?

[doughert0]

Thanks. I use a 13/17 SS prop. I top out at about 5800. Don't know why I seem slow - I use the GPS to measure my speed in kts, which works out to 28-29 mph. I rarely hold it at WOT, generally cruise at about 5000 on smooth water. I will post a photo later in the day, when the sun is right.

[doughert0]

My last reply was to McGillicuddy - hit the wrong reply button. My built in tank is 29 gallons, except that I had a 30 gallon al tank built a few years ago. I misspoke on the 42 gallons, I carry a six gallon reserve in a cruise tank, so usually start out with 36 gallons, not 40. I'll post a photo later today.

I think my cav plate may be a little high - that may be why I seem to be slow. I'll check it next time I'm on the trailer.

The consensus seems to be that a 90 will do the job if set up right. Thanks for the input.

[Texascoastalfish]

Hey Bowrider,
I have a 75 CC 20' ( 19'8" actually right ?) and I had a 84 90 Johnson which had a bad cylinder at 75 psi. I still got about 31-32 MPH on that, I sold it and now have a 1995 112 SPL Evinrude, and Im propped at 13.25 X 17 and get 37 at 5100 RPM, I need to raise Motor 1" still, but I am very satisfied with the performance. 47 gallons on fuel and 4 fisherman + Ice gear etc its a bit slower on the hole shot, but 5 mpg is OK with me. I primarily fish the Galveston Bay complex, and near offshore at the 10-12 mile rigs so out there you dont often get over 21-22 MPH safely. With 2 people 25 gallons hole shot is very good and fast enough for me at 37-38

[PipeDreamsMarine]

I run a 88spl on my 19 and I see the allmost the same numbers as you are. I'm running a 13 3/4 x 15 wheel with T&T on the motor. I hold 28 gallons in the built-in tank. I top out at 24 knots with 4 people and adult beverages.


I'm happy with the numbers

[Bushwacker]

Just to give you some more numbers for comparison, I bought a new 115 for my Seafari in 1975, when motor HP was rated at the powerhead instead of at the prop as it is now. That motor was about 90 hp at the prop. It would run about 33-34 mph @ ~ 5500 rpm running a 13.75" dia x 15" pitch SST prop. Cavitation plate was about 1" above bottom.

Something doesn't seem right here. If I assume same gear reduction in your lower unit as my old 115 had (2:1), the prop slippage calculation with your speed/rpm numbers works out to be about 38%. That's a LOT of prop slippage . . it should be somewhere around 20%!

Are you sure the tach is accurate? The original OMC tach I bought with my new 115 was off by several hundred rpm!

If tach is accurate, prop is really 17" pitch and gear reduction is really 2:1, then you really do have a very inefficient setup. Motor may be mounted too high or trimmed out too high. With motor trimmed so cavitation plate is parallel to bottom of hull, extend a straight edge back from the bottom and measure distance from it up to cavitation plate. If it's more than 1-1.5" you may be getting a lot of ventilation so prop is not getting a good "bite" on the water.