repowering 25 seafari????????

[stumpie2]

im pretty new to this site, but i have a 1974 25 seafari that ive replace stringers, new gas tank, floor 1 1/2 yrs ago, took old 350 chevy out and closed transom and installing armstrong bracket.. im kind of stuck between 225-250 merc. optimax (single) or go ahead and go thru with my original plan to hang twin 150-175 opti's either way the engine(s) are going to be merc. opti's... i dont need 90 mph but 45mph and decent fuel economy would be great... i fish the ches. bay and ocean off va. and nc. so usually i have to make a pretty good run to most of the offshore fishing grounds... thank you for your opinions

[McGillicuddy]

Greetings,
Get some pics of your Seafari up!!!
I think you'll need more than 225-250 Opti for 45mph. That boat has a 24 or 25 deg deadrise -about as deep as a v gets. I think they used to put 270 mercruisers in them but I don't know about their outboard configs - too bad they don't have a 300 Opti yet...
Maybe twin 175s but I think you'd have trouble planing on one motor. They're about 430lbs a piece, compared to 500+ for a single 225-250. I'll bet old school Mercs 175 or 245 twins @ 350lbs apiece would get you your 45...Also if you haven't already purchased your bracket, you might get some input from Don Herman (Hermco) who has done numerous brackets for the SeaCraft community. If you opt for twins, it will be especially important to get a maximum flotation bracket like Don's product offers.

Good luck. Get some pics up so my gal can catch me gawking a a Seafari 25.

[Fr. Frank]

Single 250 Optimax will only get you mid 30's for speed. And you won't plane on a single engine with twin 175s.

But since twin 250 Opti's will set you back $35K with a bracket and rigging, why not just switch the sterndrive over to 315 hp. Yanmar-Mercruiser diesel/Bravo 2 for a little less money?

(I couldn't find current prices prices on Cummins-Mercruiser, nor Volvo-Penta DP sterndrive, nor BMW Marine Diesel, and no Yamaha Marine diesel stern-drive(sold only in Asia)

[stumpie2]

well the purpose for the outboard conversion is that the old 350 i/o was geting up there on hrs and i got to the point that where it wasnt fuel effiecent enough to make those long trips any more... pics comming real soon.... merc is making a 300hp opti. on there racing website, available with normal warantee to the non-racer, standard shaft lengths... no inboard is going because as soon as i took the engine box out it was great now i can play football bck there with all that space.... maybe fish box in transom or soomething.. no engine box

[Entourage]

Yeah i like the idea of the diesel setup with the bravo drive that would be sweet. 25 Seafari is a boat that you do not want to change around too much, you may be sorry later.

[Dilligaf]

nuthinfancy where you located in va?

[stumpie2]

the boat was at sunset marina in hampton, but it is currently at my fathers house in williamsburg, choose to store it in the yard while i moved back to florida to finish school at Marine Mechanics Institute in orlando
i understand the idea of keeping the boat origanal but if you cant use the boat the way you want why have it... i have had this boat since i was 17 y.o (7 years) the first boat i purchased $2500 and love the ride and seaworthiness of the 'craft... will never get rid of it and will never stop working to get the great fishing machine that i have always wanted it is always cheaper to repower than to replace the whole rig...

[seafari25]

Welcome Nuthinfancy,

I had a feeling there were a few more out there. The Seafari 25 is pretty fancy in my book.

I'm affraid I won't be of much help as I have the same questions as you. Good thing there are many members of CSC who are experts on these topics. I haven't really pushed this topic as my old 327 still turns the wheel(as of last October) but this is something I will have to think about down the line.

For years I have dreamed about repowering with twin outboards and I think she'd look great with a Hermco bracket and a pair of 250s(cant afford it ) but after some discussion with some of the experts and the info on this site, IMO, I feel it's best to repower with the same I\O setup. Extra space in the cockpit is nice but I'm more concerned with the boats performance. I am very pleased with the performance now(and the last 30 years) and would not want to experiment and be disappointed. Not to mention, the boat has a lot of sentimental value for me and I'd like to keep it as original as possible. I encourage you to dig up as much info on this site as you can before making your final decision as there are many factors that will make or break your project (ie: weight distribution etc..). There are many things that never entered my head before finding this site.

I am, however, interested to know what you decide so keep us informed and get some pics up. I'll be gawkin with Gillie.

Good luck,
Brandon

BTW Fr. Frank, great to hear your feedback on the diesel. I love the idea of a diesel for fuel consumption but I was just wondering if there would be any weight issues.

[Fr. Frank]

There is a weight penalty with the diesel. The weight of a 1970's Mercruiser small block Chevy/pre-alpha one setup is 1021 lbs. (New 350/300 MPI w/ Alpha One is 946 lbs)

Contrast that with the weight of the Cummins-Mercruiser 4.2L ES 320hp with Bravo One drive at 1201 lbs total.

The difference between the original setup and a new 320 hp diesel setup is 180 lbs.

FUEL CONSUMPTION COMPARISONS
However the 3900 rpm (WOT) fuel consumption of the diesel is 18.8 gph, and 75% power (3200 rpms) fuel consumption is 11.7 gph, and 60% power (2850 rpms) uses only 9.0 gph. Test boat was a '99 Bayliner 2855 SunBridge repowered in '06 with CMD.

WOT fuel consumption of the 2007 Mercruiser 350ci/310hp is 23.9gph at 5250 rpms WOT('07 SeaRay 26' 240 Sundancer) 75% power fuel consumption is 18.4 gph at 4800 rpms. (60% power at 4000 rpms setting drops you to 14.1 gph)

WOT Fuel consumption of a single Mercury 250 Optimax is 27.6 gph at 6000 rpms WOT. ('08 ProLine 23' CC). 75% Cruise fuel consumption is 13.9 gph @ 4800 rpms, and 60% power at 4500 rpms burns 11.6 gph. (remember to multiply this 2X-10% for twins)

[Briguy]

Fancypants,
Welcome to the site. I have twin 115 Suzuki's on my 1979 CC. It will plane on one motor at about 14kts. I get 25.5kts at 4k and burn 10.5 gph and 38-39kts wot. In my opinion the best motor for your boat would be the 300 Suzuki if you go for a single. You'd save alot of cash compared to new 175's. The 300 would get you to 45mph nooooo problem and get 3mpg at cruise. If you want twins and don't need 50mph, twin 140's would fit the bill. I believe the twin 175's are too heavy.