Repowered my Seafari w/ a 90 hp Optimax

[Fr. Frank]

We decided to sell the Carolina Skiff, and keep the Seafari, so we took the Optimax off the back of the skiff, and just for fun, decided to try it on the back of the Seafari. So I took the 150 off, and mounted the 90.

I must admit I am surprised with how well it performed.
I only put it in the water for 20 minutes in the Withlacoochee River, but here are the first-run numbers:
ProPulse 4 blade adjustable prop, set at 16" pitch. (I don't know the diameter).
WOT 30 mph on GPS at 5400 rpm
Cruise 24 mph at 4400 rpms
Time to plane about 5-6 seconds.
Fuel flow is unknown at this time.

That's better than I used to get with a 120 hp Chrysler on this hull. What remains to be seen is how it will perform in a swell.

[Bushwacker]

Interesting numbers! Not too much different from what I got with my old "115" (at the powerhead) 1975 Evinrude. I'm guessing it was around 90-100 hp at the prop. Top speed was about 32-33, cruised at about 23-24 @ 4500 at 8-9 gph w/13 3/4 x 15 SST prop. Would be interesting to see fuel flow numbers on the Opti; my E-tec burns about half the fuel the old motor did! The 1972 brochure shows the Seafari running with an 85 Johnson! I remember being quoted a top speed difference of about 3 mph going from a 115 to a 135, and same mechanic said a 115 would outlive about 5 135's! I chose the more durable motor and ran it for 31 years with no major problems.

I wonder if one reason that folks are running so much more power these days, especially on the rebuilds, is that they're making the boats so much heavier by using plywood instead of balsa core in the decks, etc. Looked at Skip and Carla's 21 today, and under what's left of the front deck, there is a stiffening grid of 1/2 round fiberglass tubes, about 2" in diameter and maybe 1/16" wall thickness, very stiff but lightweight . . . Moesly really did build his boats like airplanes! The pictures Island Trader posted of his 21 shows floor supports between top of stringers and deck that have large lightening holes cut out of them, just like the stringers in wings of an airplane. He really understood the performance penalty caused by excess weight!

[Fr. Frank]

If I get anywhere near the fuel economy I expect, I'll probably keep the 90 on the Seafari.
On the Skiff, I filled the 25 gallon tank, then ran it for 5 consecutive days in the keys, fishing or diving every day (anchored), usually out to the middle reef, which is only about 2 miles from Bahia Honda, then we ran it 3 or 4 times on the Withlacoochee pulling a tube for the kids. Then we took it to Destin for 3 days of fishing up there in the bay. I finally refueled it on the way back from Destin, and put in 21.9 gallons. For all that.

I figure that's between 4 and 5 gallons per hour average on the little skiff. I can't wait to get some numbers, once I get my Navman reinstalled. But this may make it possible for me to actually afford fishing with the Seafari again.

[ocuyler]

My 20 CC has a 1980 85 HP Evinrude on her and she does very well. No tach or gas guage, but at WOT she'll do 32 on GPS lightly loaded and 30 heavily loaded. Nice little hole shot even with a tube full of teens behind. I see no reason for more power on this application. Gas mileage is another story, I'm afraid.

The kicker is a Yamaha 2.5 four stroke that will push her at 5.4 MPH no wind or current...

[CaptLloyd]

Fr. Frank,

I'm glad to hear you're keeping the Seafari, and you're getting to use it!!

With the numbers you're getting, I'm really thinking I need to try a 4 blade prop.

Lloyd

[McGillicuddy]

Greetings Fr. Frank and Happy new year to all,
Petrol economics sounds like a good move at least on the left coast -- $3.35/g here, today. Does that Pro Pulse prop have similar stern lifting qualities you suggested for my Seafari, or is the Optimax much lighter than the older I-6 115hp? Does the 4 blade assist in stern lift or just more efficient. Look forward to hearing what the Navman reads.

[Fr. Frank]

The Pro-Pulse definitely has more sternlift, but my guesstimate so far puts effective slippage at the 16-18% range. This is of course more of an issue when accelerating.

The 90 Optimax is NOT lighter than the 115 6cyl, it is nearly 100lbs heavier. The 90 Opti is a 1.5 liter 3 cyl, and weighs in at 375 lbs in a 20" shaft. Contrast that with my 1991 150 Merc XR4 at 396 lbs.

I plan on an extended run tomorrow to get some fuel figures. The Navman quit working after I moved the sender to the new motor. I gotta troubleshoot it. Tomorrow I'm just going to do a cruise RPM run on a 6 gal. portable, and see how long it takes to run out of fuel, then do the math. I don't have enough hours on the motor to run WOT for any length of time, so I'll wait until the fuel flow meter is working again.