Seafari 25 Conversion Thoughts on Power?

[cdavisdb]

I'm not much help on the OBs, but I do have an 8 hp Yammie hithrust on the 25. Very happy with it. Pushes the boat 4 knots into wind and chop and 5+ in calm conditions. This is far superior to the old 15 hp Evinrude I had on the Seabird. It had about zilch low end torque and would not do much at all into wind and chop, and that was with the biggest diameter, lowest pitch prop I could get. .

[Blue_Heron]

I guess I'm late to the dance... My $0.02

• My 25 had a 260hp Mercruiser (blown) when I got it. The PO said the boat would run 40mph with it. My 300HP IO will push it to almost 45 if I prop for speed and run light. Propped for normal use, it cruises at 30mph and tops out around 40 depending on load.

• I did a "back of the napkin" moment calculation once on the CG effect of a single outboard on a bracket, twins on a bracket, and a single V8 IO. Twins shift the CG aft, no surprise. A single OB on a bracket won't move the LCG aft, but it will move the VCG upward. Put a 30gal water tank under the cabin sole and call it good.

• I believe a 250 OB will be plenty of power, but it won't be a race boat. The key to low speed planing will be the prop. If you go Merc 2 stroke, get an Opti, not an EFI. The keel on this boat is deep. You will want a 30" shaft unless you like running the powerhead very close to waterline at idle.

• One advantage of an OB is engine height adjustment. My Bravo drive is mounted about 1/2" higher than recommended by Mercruiser, and it's probably 2"-3" lower than it should be. The steep deadrise angle has a huge effect on correct engine height.

[GameOnSalmon]

Originally Posted by cdavisdb

I'm not much help on the OBs, but I do have an 8 hp Yammie hithrust on the 25. Very happy with it. Pushes the boat 4 knots into wind and chop and 5+ in calm conditions. This is far superior to the old 15 hp Evinrude I had on the Seabird. It had about zilch low end torque and would not do much at all into wind and chop, and that was with the biggest diameter, lowest pitch prop I could get. .

Connor,
Awesome and Thank You that is exactly what I was looking for on the 8hp Yamaha High Thrust. I was considering trying to find a 15 Xtra Long and then Turning it into a High Thrust. That just made my day... Got a 8hp HT Yammie sitting here in the Garage.

Definately Keep You all Posted on the Build out over the next 3 weeks.

Originally Posted by Blue_Heron

I guess I'm late to the dance... My $0.02

• My 25 had a 260hp Mercruiser (blown) when I got it. The PO said the boat would run 40mph with it. My 300HP IO will push it to almost 45 if I prop for speed and run light. Propped for normal use, it cruises at 30mph and tops out around 40 depending on load.

• I did a "back of the napkin" moment calculation once on the CG effect of a single outboard on a bracket, twins on a bracket, and a single V8 IO. Twins shift the CG aft, no surprise. A single OB on a bracket won't move the LCG aft, but it will move the VCG upward. Put a 30gal water tank under the cabin sole and call it good.

• I believe a 250 OB will be plenty of power, but it won't be a race boat. The key to low speed planing will be the prop. If you go Merc 2 stroke, get an Opti, not an EFI. The keel on this boat is deep. You will want a 30" shaft unless you like running the powerhead very close to waterline at idle.

• One advantage of an OB is engine height adjustment. My Bravo drive is mounted about 1/2" higher than recommended by Mercruiser, and it's probably 2"-3" lower than it should be. The steep deadrise angle has a huge effect on correct engine height.

Blue Heron.. Thank You .. Thank You... Your calculations seem to be very close to mine. I spoke to Scott Porta today at Porta Brackets. Will be putting on a 26" 350 HP Porta Bracket in 2 weeks... Scott seems to think this is gonna be one awesome handling boat with the Single 250 on the bracket, I have to tend to agree.

I cant swing the 250 OPTI on Price now... Am working on an OX66 Yamaha from a Guy as well as a 250 Merc EFI from another. If i could swing the cash load on the Opti I would or better yet a 250 H.O. Etec that will have to come next year... The Porta bracket is almost 3k and along with Glass, Resin and all the other stuff I am gonna be 14,000 Into this sucker without much overhaul at this point. With that being said, If i can get her in the water in the next 30 or so days and run it... That should tell me where to start...

And I will be giving out all the data I can so anyone else thinkin about it with a 25' Seafari can... Thanks for taking the time to reply.. Appreciate it.

Robert

[McGillicuddy]

Originally Posted by GameOnSalmon

Blue Heron.. Thank You .. Thank You... Your calculations seem to be very close to mine. I spoke to Scott Porta today at Porta Brackets. Will be putting on a 26" 350 HP Porta Bracket in 2 weeks... Scott seems to think this is gonna be one awesome handling boat with the Single 250 on the bracket, I have to tend to agree.

I ain't doing the math, but I once used a teeter-totter at a Holiday Inn...
Might check with Blue Heron on his napkin bracket calculations. My guess is that he was including a flotation bracket in his calculation rather than a Porta-bracket.

I think Porta-brackets are fine for skinny water and shallow-draft, flat-bottom boats but me thinks this is a bad plan for a 25 deg dead-rise hull that wants is ass end out of the water in the big pool.

I'd talk to Don Herman at Hermco before spending a wad on Scott's product and ruining a perfectly good boat because a rogue wave caught your arse crossing the bar. Just a thought

[GameOnSalmon]

Originally Posted by McGillicuddy

I ain't doing the math, but I once used a teeter-totter at a Holiday Inn...
Might check with Blue Heron on his napkin bracket calculations. My guess is that he was including a flotation bracket in his calculation rather than a Porta-bracket.

I think Porta-brackets are fine for skinny water and shallow-draft, flat-bottom boats but me thinks this is a bad plan for a 25 deg dead-rise hull that wants is ass end out of the water in the big pool.

I'd talk to Don Herman at Hermco before spending a wad on Scott's product and ruining a perfectly good boat because a rogue wave caught your arse crossing the bar. Just a thought

Mcgillicuddy, Thanks for the input... The debate between Twins and Big Singles and the so called Flotation brackets vs non flotation is beat dead.

I for one just look at the math... In a so called flotation bracket you need One Cubic foot of Air to float 63 lbs... Add a 150 lb bracket you need 2.5 cubic feet... Now try and float a 495 lb engine on top of that and you need 10 cubic feet of Trapped air for balanced flotation...

I guess IMHO and it's only an opinion that Flotation brackets cannot create positive flotation... but I will say Don makes Kick Ass brackets for sure but I looked into them and between 3,000 and 4,000 bucks vs the porta with 17 Inches of verticle travel for $2900.00

The main issue is outside of one Person no one has added a bracket to the back of a 25 Seafari... I have to believe that Heron has his #'s right since mine were as close... Even taking into account the so called Cantilever effect the 600 lbs on a 26" Set back is not to far off of 2 outdrives hanging straight out the back and 1100 lbs of engines.... I am going to be really curious to see how she squats once the bracket is on with a 250 HP.

Someone here has to be a Guinea Pig and I am signing up for it... The worst that can happen... I have to remove the bracket, Notch the Transom with a 30" Foot Motor and Glass in a Splash well to Preserve the Integrity of a Full Transom...

This should be interesting to See what happens... can always add some kind of balanced Ballast to the Front as Needed to Level her out...

Thanks Robert

[htillman]

Can't wait to see the results with the bracket and OB installed and the performance with such.

[Blackfin26]

You are brave for taking this on. No expert by a LONG shot but I'd opt for a 300 hp 2 stroke on a notched 30" transom with the splashwell (make the splashwell foldable to give you as much stern room as possible). Then float her and see how she sits. From there you can add/subtract weight along the centerline as needed. Use a 6 gallon portable tank and bring weight to simulate tank placement, etc...Seems the best strategy for doing it once
Best of luck, Steve

[McGillicuddy]

Originally Posted by GameOnSalmon

Mcgillicuddy, Thanks for the input... The debate between Twins and Big Singles and the so called Flotation brackets vs non flotation is beat dead.

I for one just look at the math... In a so called flotation bracket you need One Cubic foot of Air to float 63 lbs... Add a 150 lb bracket you need 2.5 cubic feet... Now try and float a 495 lb engine on top of that and you need 10 cubic feet of Trapped air for balanced flotation...

I guess IMHO and it's only an opinion that Flotation brackets cannot create positive flotation...

This should be interesting to See what happens... can always add some kind of balanced Ballast to the Front as Needed to Level her out...

Thanks Robert

Robert,
Like I said I've not done the math, & not poo-pooing yer project. I thought the the intent of the bracket was to offset the weight of the shift aft, rather than to wholly float a motor. Which as you mentioned, offsetting the weight can also be done by shifting weight around in the boat. Obviously plenty of room to move batteries fore and store a bunch of Cannon balls up there for your salmon drops.

I'm curious about the effect of moving the 500 lbs aft 2 ft after also removing 1200 pounds of iron from the belly... seems like the vertical CG would rise some, too. I look forward to your build out thread and ensuing results.

Are you still thinking about the Tsunami? Or do you think you'll give this boat a go for the salmon and tuna excursions?

Cheers,
McGill

[GameOnSalmon]

Originally Posted by McGillicuddy

Robert,
Like I said I've not done the math, & not poo-pooing yer project. I thought the the intent of the bracket was to offset the weight of the shift aft, rather than to wholly float a motor. Which as you mentioned, offsetting the weight can also be done by shifting weight around in the boat. Obviously plenty of room to move batteries fore and store a bunch of Cannon balls up there for your salmon drops.

I'm curious about the effect of moving the 500 lbs aft 2 ft after also removing 1200 pounds of iron from the belly... seems like the vertical CG would rise some, too. I look forward to your build out thread and ensuing results.

Are you still thinking about the Tsunami? Or do you think you'll give this boat a go for the salmon and tuna excursions?

Cheers,
McGill

Mcgill,
I am definitely giving the 25 a go for salmon/tuna runs this season. I have a sneaking suspicion this is gonna be a "Different Kind of Project" then things I have tackled in the past. Normally a guy can gather some field data to base some decisions on....

Today as we both noted it's nothing more than pure Theoretical Speculation on my part. I am 100% convinced a Notch Out with a 30" shaft and Splashwell conversion will work Great. But I have always used some form of Hydraulic/Electric transom jackplate and the performance has always been steller. In fact I installed a 20" Gil bracket with a Transjack a few years ago on a 22" starcraft Islander when Guys said i was nutz... Was one of the best performing aluminum boats i have ever owned for big water... But it wasn't no Seacraft...

At the end of the day... I am doing all this work with the hopeful intention of keeping this 25' til i Keel over and then be buried in it. Now that I am committed its gonna be pretty cool to see what happens... I mean Hell, I think a 250 Single should push this monster 44mph to 48mph at WOT but I could be wayyyyyyyyy... Off on that. I think a lot of guys get engine mounted and prop and call it good. I am a fanatic about engine height and Prop Selection and amazing things can happen when you get the 2 dialed in correctly for any give boat.

Thanks again for the input always appreciate the fact that anyone takes time to reply on a forum thread. Will start the Build Thread as Soon as I get the Seacast, Mat, resin ordered and of course the Porta bracket...

Regards,
Robert

[Blue_Heron]

Originally Posted by McGillicuddy

I ain't doing the math, but I once used a teeter-totter at a Holiday Inn...

Gillie,
The IO is the fat kid that sits closer to the fulcrum on the teeter totter to make it balance, the bracketted single is the skinny kid sitting out at the end. Bracketted twins are the fat kid sitting on the end of the teeterr totter, and a non starter for balance.

Dave