25 seafari
 

need help what would we need for power on a bracket not looking for speed twins or single how will the boat performe with bracket thanks

George - I think you'd be fine with a single 250. Sonewhere there was a post from bigfluke about a 300hpdi and a porta bracket on his 25.

We tested the Seafari at weights from 4200 to 7400 lbs and with lcg's from 27% to 37% so handling isssues happened under many different circumstances. Our first tests were to develop a novel drivetrain with a 480 hp Yanmar and Weismann surface drive and we achieved 45+ knots @ 7400lbs. Current test configuration is with 300 hp Yamaha outboard on a Porta bracket. Our focus has been to move lcg as far forward as possible to improve pitch behavior without compromising following sea handling. Our hydrodynamic tricks to the hull bottom have been focused at reducing the increased drag which comes with a forward lcg. We have already yielded a 3+ knot improvement in speed and expect to see +5 knots on the next experiment. The info that Moesly had intended a ballast system makes a lot of sense from what we've experienced in running the boat with lower and further forward lcg. The basic boat has outstanding seakindliness at all headings when weight and lcg are dialed in. When we finish all of our research we expect to see a 15% improvement in speed/power and elimination of the handling problems that are inherent in many narow, deep-v hulls with fine entry. I consider Moesly along with Hunt, Hickman and Lorne Campbell to be creative innovators who have made major contributions to planing hull technology while achieving balanced and producible designs. I am delighted to have learned that Moesly planned an integrated ballast system which would have eliminated the sub-par performance issues with the Seafari. I'm sure if he had continued the development of this boat it would have truly been an outstanding performer and benchmark for its size.

http://www.classicseacraft.com/commu...t=18368&page=4

I believe the boat came with twin 165HP inline 6 I/O's. From my understanding the boat is narrow and with the deadrise HP was an issue. It will take as much as you can afford, twin 200's would be very good but a single 300 if you find one should work as its much lighter than the old I/O's. I think the sheer weight of twin I/O's was the issue with the ballest system, they just didn't have the power plants available to make it work right. JMHO - had a buddy that dove off one but never rode in it.

Can't comment on outboards, but 300 hp in an I/O works fine. I get about 25 knots medium load at 3400 rpm with a 300 hp 350/volvo duoprop. The boat jumps out of the water in a hurry when you hit it from idle. Speed drops pretty fast with weight added, more like 23 knots loaded heavy.

Even with a much lighter power plant than the twin 165's, the boat still likes more weight forward, especially as fuel gets burned. Seems like an outboard on a bracket is going the opposite direction. Putting a substantial water tank under the deck in the cabin, like Strick and Blue Heron are doing, might be a good thing to do with an outboard, helps lower the CG as well.

the boaT HAS 140 4 cyl chevys would like to know how boat ran with them anyone know? maybe i should rebuild them have good comp all cyl but water jackets need to be redone getting ready to do transom need help making up my mind?thanks

25 Seafari
 

Shana, you're wise to ask about the CG shift with various powerplants! Connor is right, in that a bracketed outboard will shift the CG aft unless the outboard is a LOT lighter than your current sterndrive configuration, which probably has the majority of it's weight forward of the transom. If you go with a bracketed outboard, I'd pick the smallest setback you can live with along with the lightest motor. A big flotation tank helps keep the scuppers higher at rest, but it's irrelevant when you're up on plane since the tank then has no effect on CG.

Not sure this is true for the 25 Seafari since it was not built as designed (with the ballast tank), but Moesly located the fuel tank right on the CG for all of his designs so they wouldn't change trim as fuel was burned off. (He was a veteran military transport pilot, and pilots understand the impact of CG on vehicle performance better than anyone else!) If you assume the CG of your current configuration is located at the center of the fuel tanks, it's pretty easy to calculate how much the CG would shift (in %) from it's current configuration with a given powerplant. . .

First calculate the total moment about the CG (weight x distance from CG) of your B/M powerplant: Moment (B/M) = (total engine wt x distance from center of engine to ctr. of fuel tank) + (total outdrive wt. x distance from transom to ctr of tank) = XXX lbs-ft.

Then do the same for the outboard: Moment (OB) = (Motor weight x (distance from transom to tank ctr + bracket setback distance)) = YYY lbs-ft.

If the YYY number is 10% larger than XXX, then the CG would shift aft by roughly 10%, etc. If you know everything but the outboard weight, you could set the 2 equations equal to each other and solve for the weight of the outboard needed to avoid a CG change for a given bracket setback! (They're typically 30") Denny

I haven't had my 25 in the water yet, so I'm just drawing conclusions from the information shared by other Seafari Owners. But this hull is supposed to be a little tail heavy, and maybe a little top heavy. That's why Mr. Moesly designed the ballast tank system for it.

Stern drives are heavier than outboards, but their center of gravity is located forward of the transom and below the waterline. Outboards are lighter, but their center of gravity is behind the transom and above the waterline. Put them on a bracket, and their CG is WAY behind the transom. That just seems like the wrong way to go with the weight distribution for this hull.

I did a little math to see what effect different engine configurations might have. I had to make a few assumptions, some of them just WAGs, but here they are:

* The CG of the 25 is 8' forward of the transom heel, per Bigfluke
* The CG of bracketed outboards is about 40" aft of the transom (30" for bracket, engine CG 10" aft of that)
* The CG of a V-8 I/O is about 16" forward of the transom.

A Yami F250 weighs 562lbs. Multiply that by a moment arm of 11.33', and you've got an aft pitching moment of 6369 ft lbs.

A Mercruiser 350 Mag MPI/Bravo 1 weighs 1044lbs. Multiply that by 6.67' and your pitching moment is 6963 ft lbs., about 10% more than the single F250.

But stick a pair of 150 Etecs on a bracket and you've got 866lbs x 11.33' = 9811 ft lbs. That's 54% more pitching moment than a single F250, and 40% more than the I/O.

If my miscalculations are anywhere near correct, a single outboard, even a big one, won't be a bad thing for longitudinal balance, but even a relatively light pair of twins is going to throw the balance in the wrong direction.

It seems obvious that switching from I/O to outboards will raise the cg. I won't even attempt to calculate how much, or what effect it might have on roll characteristics, but it seems to me that a deep V hull with a very narrow beam is going to be a lot more stable in the roll axis if the cg is as low as possible. Switching from I/Os to outboards takes the vertical cg in the wrong direction.

My $0.02
Dave

P.S. Denny must have entered his post at about the same time I started writing mine. Same principal, I did some guessing on the math.

Man you guys are way above me on this one!!!! I understand the principles, however too much math for 'ol Jethro!

My brain hurts. :)

thanks gives me a lot to think about if i could get some input from who has their 25 seafafri in water and running what do you have for power?this mite help me thanks for all the help

I've put about 300 hours on mine in two years, both inshore and offshore, mostly diving. Power plant listed above.

Let me first qualify my comment by saying I have ZERO experience with a 25' Seafari, but with everything I've read here since the site began in 2002, it appears some members know A) a lot about CG and boat design, and B) know a lot about this particular model. Now here goes my 2 cents...stick with an I/O config in this boat seeing as that is how it was designed. There weren't any OB versions ever made from the factory, so you're in for a lot of unknowns with switching to a bracketed OB. We can all argue the pluses and minuses of both OBs and I/Os, but it appears to me this boat was meant for an I/O (either single or twin) and should be left that way. Stepping off my soapbox now...

IMHO, CG, both vertical and horizontal, is pretty important in these boats. Bigfluke noted that the CG (I assume with the orginal twins) was farther aft than usual. He got his best performance moving the CG forward and adding weight. My boat is lighter than original by about 500 lbs due to going to a single I/0 and not tail heavy at all. Changing power plants moves the CG forward, but mine still likes more weight forward, especially when running light. When coming home from a long trip, light on fuel, water, ice and groceries moves the CG aft, one big guy moving from the engine box to the steering area makes a big difference in pitching and seems to increase speed.

Vertical CG greatly affects rolling. My experience with deep Vs is that those with very low CGs are reasonably docile lying in the trough. High CG deep Vs can roll your guts out. The seafari 25 is not as bad as some, formula 23 for example, worse than others. I've been very careful not to add weight up high. Also, when light, my boat easily rolls the outboard hull panel out of the water at the stern, accentuating the roll. That is not as bad with more weight in the boat. I'm planning to do some stuff with bigger trim tabs to try and damp down the roll.

I'm thinking along the same lines as ScottM.

A bit rambling, hope this helps.

Just a guess on the 140s, 280 horse power with two drives will be significantly slower than my single, but faster than a 25 Bertram with twin 130s( a much bigger, heavier boat). 18 knots most efficient cruise on the Bertram, 23-25 knots on my Seafari, guesstimate on the 140s in a Seafari 25: 23 knots medium load, 21 knots heavy, lots and lots of wonderful torque. Prop selection will be critical.

I honestly think that trying to work with the old motors is a mistake - it seems you are always chasing some new issue and the parts eat you up =twin drives as mentioned are a big negative as well. You have to understand the limits of the power available back then, I would bet if he had todays outboards they would have come with that option, the V6 175 Merc did not come out until 1976.

Wouldn't a bracket help somewhat with roll -
kinda like a trim tab ?? as we all do on our boats a good deal of weight could be moved forward - like batteries.






Also seems cutting weight in half would have to make the boat less tail heavy - I'm kind like Don though as I have never been accused of being a rocket scientist, many other things but that wasn't one of them.

George,
I have to agree with Scott. His post pretty much mirrors my thoughts when I made the decision to stay with the I/O.

I also agree with ESD on the engines. If you're going offshore, and that's what this boat was made to do, you don't want unreliable power. If you can go through the engines and outdrives, and you're sure they're reliable, go for it.

I know there are some 25s out there that have been modified for outboards. I've seen them for sale with brackets, and one with a transom mounted outboard. But I don't know of any members here running a 25 Seafari with outboards, so it may be difficult to get real world feedback on that option.
Dave

one thing about the 4 cyl motors is there is a lot of them around had many boats in the past with them only as singles never twins one was on a johnson boat and it was a heavy boat a little slow out of the hole but was ok thanks your all a big help

The boat was marginal with inline 6's, if your going to be doing much work and/or spending money I would do something else

An e-mail that was forwarded to me by Bigshrimpin several years ago regarding the 25 Seafari power options as told by Mr. Potter:


Hi Tim,
Please tell Strick he has the best riding SeaCraft we ever built. It is not a boat for someone who doesn't know how or doesn't want to use trim tabs and the power trim of the IOs or outboards to get the most out of the hull design. The boat has the deepest V (25degrees) of any SeaCraft and, due to having no lifting strakes, it is more sensitive to "leaning" in cross winds and from weight shifts while on plane than other SeaCrafts and other deep Vs. BUT, it is like flying an aerobatic plane, if you know how to use the trim you can set that boat up to run through anything you have the nerve to be out in with remarkable comfort and safety. AND, because of the Variable Deadrise Hull design it is a very stable platform at rest or at trolling speeds. I wish we had a recording of the story a guy told us about his run from St Croix to St Thomas during a major hurricane flying through and off 25 ft and larger seas in the dark! Pigs don't fly!
Best regards,
Bill Potter
ps A SeaMark twin Fiberglass Bracket and properly positioned and operating trim tabs would be my recommendation unless he is going to go with a big single diesel duoprop stern drive or smaller twin duoprop sterndrives. ( Duoprops minimize torque roll)

strick

strick thanks for the reply very well worded will take what you send and think hard on it money tight and dont want to do it the wrong way thanks george