Here's a post I made at The Hull Truth, trying to organize my thoughts and get some input on repowering our boat. What do you guys think?

Well, it's time to repower our 28x10 aluminum offshore boat. It's currently running 2006 200HO Etecs and we're switching over to Yamahas because there's no Evinrude service in our area. I've been debating how to set the boat up with 4strokes and thought I might solicit some advice.

Here is a picture of the boat the day it shipped, just to give and idea of size & type:



Here's another shot which shows the hull profile & V, as well as the Etecs.



The boat cruises at about 27kts on good water, running right around 4000rpms. It will get on plane on one motor with the other trimmed up out of the water. It's running 17inch rebel props. I don't have any fuel burn specs, unfortunately. I believe the boat to weigh between 9000 and 10,000lbs with average load. Fuel capacity is 190gal and fresh water is 35gal.

I've discussed the repower with our Yamaha dealer, who offered thoughts on a couple choices -
1-single F350 (I really like having twins for safety's sake offshore). Our boat is very similar to this one, so I can get some idea of performance- http://www.yamaha-motor.com/assets/p...os-f350tur.pdf
2-twin 150's (I hate to drop down 100hp, especially going from 2stroke to 4stroke; don't think I would be happy with the performance but fuel economy would probably be pretty good if I could stand slow cruise speed)
3-twin 200's (these are a bit heavier than I would like and I figure if I'm gonna go this route, might as well take advantage of the new, larger displacement 225's)
4-twin 225 offshores (my current choice)

After reading lots of performance specs on the new offshores I am thinking the twin 225s will be a good match for the boat. The weight difference is only a slight increase from the 2006 Etec 200HO and the additional displacement, plus a touch more hp should help offset the holeshot difference. Also, there appears to be some fuel efficiency gained with the new offshores.

The 225 offshore seems to be a good match for the boat. I could go twin 250's or twin 300's, but don't really see the need. I am guessing with the 225's I will be seeing something like a 28-30mph cruise at something like 3500-3750rpm and probably burn around 16-18gph. I know this is a wild-ass guess but I've pored over so many performance charts of different configurations with these motors I feel like it's a reasonable stab at a prediction. Only time will tell.

Anyway, what do you guys think of my reasoning and do you see any holes in my logic?

Thanks!
Dave

I'd go 250's no doubt. Same weight, more HP, motors shouldn't have to work as hard.
Where we fish almost all the guides that fish every day run 250's and have been for years.......

i like the way you think...

When starting from scratch, never go under powered...........grin

hard to believe it will be underpowered with 450hp given that it already hauls ass with 400hp but your point is well taken.

can never have too much hp

4stroke torque is not the same as 2stroke.......

Definitely true. However a big displacement increase helps with that. The new offshore series is 4.2L vs the etec 3.3L.

I just repowered the skiff from 2stroke 150 to 4stroke 150 (both Yamaha) and was able to clearly observe the differences between the lighter, torque-y 2stroke and the heavier 4stroke, both of the same hp. It is an interesting comparison on the water.

I'm guessing bigger displacement, 50 more hp and virtually same weight will help balance the issue in this case but probably won't erase it...

All of which, under consideration, helps pass the time at work...grin.

What's even more interesting and will make you think is that the "150" 4 stroke Yammie actually has 172 HP.........

And still won't run with a 2 stroke..........

I didn't know that. Underscores the difference, for sure...