Powering my 23 Seacraft

[Mayco]

Hi Classic Seacraft owners. I recently purchased a 75 23 Sea Craft. I will be closing the transom and placing an Armstrong bracket. Ideally I would like to have the boat get to 58/ 60 mph top speed. I have spoken to few Sea Craft owner and opinions seem to vary. Some say this boat hull was designed to be able to go these speeds and was raced in 1970s at speeds greater than 60 mph. While some say past 50 mph boat gets hard to drive and steer as it is barely in the water. This is my first Sea Craft and really want too make sure I power it correctly yet get biggest outboard on it yet keep it safe. I am going to place a single motor. I see in old brochure boat had max motor hp at 500 hp but my guess is that's for I/O . Does anyone know what the speeds would be with a 300 Merc/ Yamaha ? I have heard that a 300 hp would probably be best fit and should get 23 foot to about 55mph ? As anyone ever had a 350/ 400 Merc outboard on a 23 foot and if so how did it perform and drive.
Thank you.

[Old'sCool]

My '73 23' with Hermco bracket and Yamaha 300 would run mid 40's. If I built another 23', I would exclude the bracket.

[Fr. Frank]

I would like to have the boat get to 58/ 60 mph top speed.... Some say this boat hull was designed to be able to go these speeds and was raced in 1970s at speeds greater than 60 mph.

The 21' hull achieved low 70's with triple inline 6 cylinder Mercury outboards nominally rated for 110 hp each, which Frank Brown managed to get to put out around 180 hp each. The 23' hull in racing was raced with triple inline 150 hp Mercury outboards turning 9000 rpm and putting out between 220 and 240 hp each. It ran with a top speed in the mid 70's, as I recall and Frank Brown said he once got it to 77 mph over a measured course.

While some say past 50 mph boat gets hard to drive and steer as it is barely in the water.

That's absolutely true. Because the VDH hull has no horizontal flat planing surface, and very high speeds it's riding solely on a single pair of angled planing surfaces. Hydrodynamics makes it want to fall off onto one side or the other for minimal water resistance. Taking ANY SeaCraft hull above 50 mph without trim tabs to stabilize chine walk is very dangerous and extremely hard to control. I once had a 23' SF with twin 235 Evinrudes. I installed K-planes to avoid a constant oscillation from port to starboard center planing surfaces. FTR, with the K-planes, low-water pickups and proper mounting, turning 32" pitch choppers, that boat would occasionally be able to touch 71 mph, or 61 kts.

I see in old brochure boat had max motor hp at 500 hp but my guess is that's for I/O . Thank you.

The 23' SeaVette and the 23' Savage were both rated for 600 max OB hp for a couple of years when Mercury came out with the 3.4L big block V6 (300ELPT and 300XLPT) in 1983/84. You had to request that placarding from the dealer, though. (I was a SeaCraft dealer during those years.)

[77SceptreOB]

I have a new 300-V8 Merc on a notched transom. With a 300hp 4-stroke you can expect a 50-53 mph WOT depending on the set up. I've seen the 350 HP (bigger/heavier) single motor guys report 55-56 mph WOT. If want a true 60 mph 23' SeaCraft you would probably need to go with a 400 Merc Verado or Yamaha 425-V8, both pretty heavy motors. The ultimate answer would be a Merc 450R (Similar weight to the 400 Verado and significantly lighter than the Yamaha 425-V8), but that is probably a $60K motor. But it would certainly get you in the 65+ mph range, probably closer to 70. Thats a scary speed for a 23' SeaCraft with a VDH. Maybe possible with K-planes as mentioned above.

[Mayco]

Thank you for your feedback. I will probably end up with a 300hp/350hp!

[joshmon71_capecod]

I had a 250 Verado, supercharged that was a wee bit under for turning a 17P Rev4. I was told the 15P Rev 4 was not worthy dont know why. Chipped it to 275 and was perfect. Super charged by factory engines, boats and cars, are often just ecu controlled for HP. Now have a 300 non supercharged Verado and love it. Can turn a 19P Rev4 easy peasy. I have a Armstrong bracket. I would not run a 600lb+ engine without a full float bracket myself. and tabs. now mounting tabs with a full bracket, non raised deck and scuppers, was painful. Speed is high 40 mph's wide open with 300. I have a T-Top...acts a like a sail I theorize. A pilot house or such with enclosed to wind in front facing surfaces, should get more speed-o.