View Full Version : Twin outboards on my 28 sportsman ????

10-02-2011, 07:21 PM
thinking of repower with twin outboards new 4 strokes ... any one already done it ??? how much HP .do you think it will take to push her ???

10-02-2011, 10:09 PM
Two of these would be interesting . . .

Rated Power
557 hp @ 5400 RPM

Rated Torque
550 lb-ft (745Nm)

Engine Construction
All aluminum

Engine Configuration
90 degree V8

6162cc (376ci)

Bore x Stroke
103.25 x 92mm

Compression Ratio

Induction System
1.9 L TVS supercharged and intercooled

Cooling System
Closed loop

Fuel System
Returnless center feed Multi-Point Injection (MPI) with stainless steel fuel rail

Maximum Speed
5500 RPM

Integrated hydraulic power steering




10-02-2011, 10:38 PM
wicked .. i bet the price is wicked too ... who makes it

smidgen too
10-02-2011, 10:45 PM
Seven Marine makes it, they start out with a new dry sump Corvette engine .

10-02-2011, 11:30 PM
A whole new meaning to "vette motors"....:)

Just Say N20
10-03-2011, 09:45 AM
I thought they were the supercharged Cadillac engines. Priced "around" $70,000 each.


joseph m. hahnl
10-03-2011, 05:15 PM
thinking of repower with twin outboards new 4 strokes ... any one already done it ??? how much HP .do you think it will take to push her ???

HIGH LIFE "Rest his soul" Had twin 300 pro max's on his 27 Magnum.

So far I got 78 but was only turning 62-6400 RPM need to hit 6,800 ! Need to send props out to get max rpm this winter. Last year I got 71 w/ Pro Max 300 @6,100 rpm. "HIGH LIFE"

10-03-2011, 08:35 PM
These also look nice....I wonder what the price tag is ?




10-03-2011, 08:47 PM
I just have to win the lottery this week....:shades:


joseph m. hahnl
10-04-2011, 08:02 PM
Fixx, according to the Eye witness's there was a little more involved then just the deck separating:garfield:. But you are absolutely right. Certain precautions should be taken when modifying something beyond the design intent. But I personally don't think that 560 Hp was overpowering that Magnum. Two Mag 350's would roughly be the same.


10-05-2011, 10:53 PM
Outboards the the stern of a boat that was originally designed as a Vee drive . . you have lots of work ahead . . . complete structural rebuild of the transom and you'll need to rebalance the whole boat when you're all done.

Adding this amount of weight off the stern will greatly effect how this boat handles waves and big water. The propulsion point will be much further astern, weight will be way behind the boat and it may want to stand on it's stern in rough water . .

There are some that believe this played a big role in Mike Spirito's death (High Life). His boat was not going extremely fast when it hit a cruiser wave and launched the bow to the sky . . Do some research and you'll find many many pics of Magnum 27's flying high in huge waves, these boats are known for rough water capabilities and flying level.

A 28 Donzi as built will handle huge water with grace and agility, it may not be the fastest boat out there, but you have to consider that the design is from the early 60's. If you have a nice 28 Sportsman, repower with something a bit more in period with the boat . . twin big blocks and Bravo drives . . set the X dimension higher, add K planes and prop it right . .

Mario L.

68 Magnum 27
69 Corsican

Greg Guimond
10-06-2011, 03:35 AM
Any boat can be converted to OB but 9 out of 10 times the costs far outweigh the benefits based on the design of the hull in question.

10-06-2011, 02:00 PM
If money is not an issue, consider scissor jacks instead of a bracket. Eliminates jackplates and moves engines closer to transom or farther away. Probably the same money if you make a bracket and do hydraulic plates. The money problem comes from the engines. Twin 300's will be at LEAST $15k ea not to mention the "little" stuff. Then again you do see the used set for $15k which could be a good alternative but still $$.

10-07-2011, 02:01 AM
you wont get "good" 300's for $15 K each new. 200 Etecs are around $15K from a reputable dealer new "plus" rigging. you also dont need 300's on that hull. Twin 250 Etecs would be more than enough and it will run fast with plenty of mid range power. i'm running a 200 Etec on my 21 Northrip and it's pushing 46+ with more low and mid than i could ever imagine, for a fishing boat of course.

10-07-2011, 10:15 PM
True if you consider Suzuki and Yamaha not "good" engines. I live in FL....$15k is not a problem except for Verados which are a repower nightmare anyway.

10-07-2011, 11:03 PM
I dont know about you but i know from first hand experience that yamaha and suzukis are good engines as i am in the commercial fishing business and buy more yamahas than you have probably ever seen. i just shopped 200-300hp outboards and all the 300 hp "good" motors "new, from reputable dealers" as i said, were running close to $20K that I found. Maybe i should have checked Florida? 150 hp yamaha 4 strokes and 200hp etecs were running north of $14K plus rigging. my main point was that 300's are overkill on that rig.

10-08-2011, 12:19 AM
Could be overkill. Never been on a 28.

Next time shop FL. I can get 150 E-Tecs for under $11K. 150 Suzuki/Yamahas for about a G less depending on warranty. BRP are proud of their prices. I paid $5995 for my 115 Suzuki out the door. Gotta love this state.

10-18-2011, 09:57 PM
the idea is to get some kind of fuel efficency ..the new four strokes on boats of this weight are getting 2 MPG maybe more ..i just cant afford to feed the twin 454s in her now .i have to run 50 miles off shore .. plus 30 or so miles while i am out there 130 or 150 mile round trip we spend a night or 2 to make it worth the time .. i get maybe 3/4 of a mile to the gallon now .. outboards could double or triple my range dont sound like alot but .. it would get me 2 trips for the price of one .. i am currently doing exactly this to a 25 bertram that was a v drive other bertram owners have completed the conversion and get 2.2 to 3 MPG with single outboard 250 hp fourstroke

10-20-2011, 01:16 AM
Based on the fact that you are going to run 50 miles out and back plus trolling miles the fuel efficiency is only 1/2 of the consideration. Reliability of the yamaha 4 strokes, to get you back, coupled with the fuel savings of at least 30% over the big blocks ( depending on which big blocks you are talking about it could be much more ) is a slam dunk. The 29 im looking to rig is going to be hanging twin 300 yamahas on a 7100 lb dry weight hull. It will run 60 mph plus and will be fuel efficient as anything out there plus reliability second to none which makes it a no brainer. Dealer cost is about $40K a pair. Big blocks are not designed to run hard for 50 miles out and back, 4 strokes are, so life expectancy of the 4 strokes will be 10 times longer than the big blocks. If you got the bread, make the investment. If not, watch ebay, pairs of 250 yamahas or suzukis ( that should be plenty if you hull weighs what I think and depending on what top end you are looking for ) come up more often than 300's and will save some good bucks over new. if you can swing new, do it. When I'm 50 miles out, piece of mind is everything!

10-20-2011, 02:33 AM
Just brainstorming a little--how about a pair of Volvo 220 HP diesels with duoprops? A mere 800 lbs apiece including the drive weight. Can probably get a pair for $45k, if not a bit less. None of the structural concerns about having the weight hanging off the transom. Diesel efficiency at cruise and trolling. I'd think not too much heavier than the outboards. Meant to run at maybe 3/4 or more of max RPM continously I'd think.

Way expensive parts. Not good if you don't run the boat much, but I'd think a possibility if you put a lot of hours on it. Might not be enough juice, I suppose.

Just an idea.

10-20-2011, 09:22 PM
That's also a good choice. I ran a Volvo KAMD 42 / 230 hp in a 26 cc Albemarle which was over a 7000 lb boat and she would burn about 4 gph average. That's running offshore to the Rock Pile, NC, trolling all day and running back in. About 100 miles all day. You will also get a 1000's of hours before rebuild if you take care of them.

10-21-2011, 03:43 PM
comparing a 28 sportsman to a magnum is not really fair. the sportsman is a much bigger boat with a rounded keel, a beam that is more than 2 feet wider and a gross dry weight that is 2900 lbs heavier.

I don't think it is going to know that there's two eggbeaters hung on the back, as long as the transom is strong and setup correctly.

10-21-2011, 04:06 PM




10-21-2011, 10:52 PM
does anyone think a single yamaha 350 four stroke would push my 28 sportsman

10-21-2011, 11:30 PM
A single 15hp Yamaha would "push" your boat.....how fast ya wanna go brother?

10-22-2011, 10:18 AM
sounds like your boating style might be better served by the security and redundancy that twins provide.

10-22-2011, 10:24 PM
yea twins have advantages ... but a new single and a sat phone should be close second .. with a single i would also have a 15 hp aux kicker ..epirb of course and lift raft .. ive been diving the gulf for over 25 years.. several diiferent boats .. lots of commercial trips hell i even worked a couple of years on a shrimp boat .. but now when your grouper limit gets reduced every year .. range and fuel consumption is much more important ..

10-23-2011, 12:11 AM
i know alot of guys running 23 regulators with the 350 yamaha 4s and i've made plenty of trips as well in my single deisel albemarle. if its all you got to work with you go with it and watch the radar. i've fought my way in on crappy days when i pushed it and the sat phone did'nt make me feel much better about my situation if the ****e hit the fan. the purpose of the single 350 was marketing not practicality. ask any one of the guys running single 350's offshore which setup they would prefer and every one would go with twins. when they bought they were on a budget, no other reason. i'd buy 2 used low hour 200's before a new 350 any day of the week. 150-200 hrs on a pair of 4s 220 yamahas is nothing and would be close in price. or, spend the extra 10K and go with new ones. 200's should plane it and give you a respectable top end which is of little importance anyway with your intended purpose.

10-23-2011, 10:28 PM
twins it will be ill keep my eyes out for a pair of good used 4 strokes