23" Scepter I/O performance

[pelican]

Originally Posted by BigLew

Pelican,

So, what is the ride and performance like? Before and after, if you can add some dimension to that would be great. How much fuel is on board? Other factors?

Also, what are we talking about, "a little tweaking"?

ride's the same - performance is the same too - lost about 1kt on the top end
boat's normally ran "heavy",with a full load of fuel 150g
previous wheel was a merc mirage 3 blade

"tweaking" - the engine would turn the rpm i wanted,the whell went to the prop shop for some tweaking,to get the rev's i wanted.the boat will run faster,with more pitch in the wheel...

[Water Rat]

Originally Posted by BigLew

Happy New Year to all.

I was out with the dog this morning and looked over at my Scepter that I fervently hope will become a WIP (work in progress) soon. She has a 140 gal fuel tank, tabs, etc.; much like most others. I have a 260 HP volvo penta out drive on it and intend to keep it that way. I DO intend to replace the motor however and am thinking about taking up over 300 HP. Someplace between 315 and 350 depending on whether I go normal carb (somewhat repairable on the water if it should fail) or Injected (which I understand little about and less in terms of repair.) I likely may adust the fuel tankage to something a little more realistic for my purposes, say fore and aft mounted dual tanks of say 80 and 50 with the smaller mounted aft and not kept empty unless I should feel the need to carry more fuel at one time for whatever reason. By my calcs that would give substantially over 200 mile range. I live in norhern Mass. and would likely not venture more that 40 miles offshore, but I may venture as much as far down to Long Island/New York or up to Camden, ME.

My question is what are real perfomance numbers for various power options. It is no speed demon, but in the past I was cruising at 21-23 @ 3200 RPM and about 32-34 WOT. That may have been a bit conservative, but the extra two carb barrels weren't open at cruise and I was getting about 5-7 gal/hour burn rates overall.

I hope to hear from all and I wish everyone of us a better year, no matter what your 2011 was like. Be well!

BigLew,

Sorry I'm late to the party but happy to share my thoughts. For comparison, I have a '78 Sceptre with a 7.4L Bravo One, and a full cored-glass half-tower, EZ2CY enclosure with radar arch, riggers, etc. (definitely adds some weight compared to the bimini/3 sided enclosure on before).

First thing I would check is to see if your drive can handle the additional torque of the motors you are talking about. I have some familiarity with the Volvo's, but not as much as Merc; I do know you would not want to mate any of these motors with a Merc Alpha 1 drive by comparison.

With respect to your tankage, I have two tanks also. My aft tank is around 65 useable and the forward around 45 useable. I would strongly recommend the larger tank be aft and here's why. Others here have said the Sceptre/Tsunami I/O sits and rides differently and it does. The CG on these is considerably farther forward than the CC's, especially with a hardtop and a bunch of gear in the cabin. I typically burn the fuel in my forward tank first, then use my trim and/or tabs to bring the bow further down if conditions warrant to compensate for the reduced weight up there. Works especially well on a long trip; when I suck air on my forward tank, I know I've burned less than 1/2 my capacity and I also would not want the forward tank full and the aft tank empty if I had a long way home in a big following sea.

As far as performance numbers, I may not be a good comparison. My 454 is carbed (4bbl Quadrajet) and I'm pretty certain I'm due for a carb rebuild on top of having a vacuum leak somewhere (almost 1900 hours on this block now). Between that and using my tabs a lot, my performance suffered a bit this past season (need to get a good mechanic to go through my motor - I am not one). That said, at 3000-3200, in calm conditions and depending on load, I will cruise at 22-24 knots burning 10-12 gallons/hour. 3500-3600 gives 26-28 knots, and I'm guessing 15-18 gallons/hour. If it is snotty out and I'm using a lot of tab (I have the big Kiekhafer K-Planes on my boat - like dragging two five gallon buckets behind the boat when you have them down more than a bit) all these numbers fall apart and get ugly quickly.

I think a 5.7 or 6.2 litre block, at the higher horsepower ratings, would do very well in your boat. I would not be afraid of an injected engine, you just need to educate yourself with it, and would be very careful to consider the torque and torque curve. Ideally you would find a motor that is very strong torque-wise at a cruising rpm of 3000 or so.

Or you could spend your kid's inheritance and drop in a Cummins QSB with a Konrad drive.

Good luck and feel free to ask me any questions.