[chriswufgator]

Artwork, I think over time you'd probably be happiest sizing the diesels appropriately to the boat's intended cruise speed (18kts or so), and then increasing the prop pitch over normal and only using the power to go 9kts if you want to.

You're already committed to diesels, and the cost difference between the T 300-350hp the boat should have and the T200hp you are talking about putting in is negligible, compared to the total cost of the repower.

Your fuel consumption probably won't improve significantly over powering the boat appropriately to its design and then running at 9kts, especially if you tweak the situation with bigger/higher pitch props.

The fact is, you can't turn a roamer into a trawler. The engine setup in trawlers is only a small part of the equation. Most of the reason why they get 2 or 3GPH burn at 8kts has to do with the full-displacement hull shape, the stability given by the keel, the total lack of any chines, the gigantic props and huge reduction ratios, and the fact that they are generally single-engine with propulsion mounted at the centerline. It is an efficient hull design to push, whereas your Roamer is significantly less so.

With your Roamer, though you can increase prop pitch (recommended), you will never be able to have trawler-sized props...they just won't fit. Additionally, the hull has hard chines, has no keel, and has twin engines driving two counterrotating props. That setup is never going to be as efficient as it could be, because the designers factored in a benefit trawlers do not have...the ability to go 18 or 20kts.

While you may get some negligible improvement in fuel economy at hull speed (I'm guessing maybe 2 gph, but also potentially 0), reducing the boat's engine capacity to that extent is really only going to give you a negligible difference in fuel economy (if any), while robbing you of the ability to plane out. With twin 200hp diesels, you *might* see 12-13kts going downhill with a tailwind, and you'll be burning pretty much the same amount of fuel at your 9kts cruising speed as you would be with the larger engines anyway, since all you are really doing is putting in a smaller engine and running it at a higher percentage of its capacity instead of putting in a larger engine and running it at a lower percentage of its capacity.

Think of it this way: It takes the same amount of motive force to push the boat at a given speed, regardless of what engines you install. That will generally translate to the same or similar fuel burn, unless you start changing variables other than just engine size.

Fuel-economy wise, I'm afraid it all comes out in the (prop) wash. Your problem isn't the power, rather it's the hull-design, which isn't particularly efficient. Personally, I think you're going to screw yourself on resale with the smaller engines as well. Your boat will be a lot less desireable on the market, being so underpowered, because you're excluding 99% of the potential buyers. Think about it...people that are really concerned about fuel economy are going to go and buy a single-engine grand banks or a marine trader or somethig like that. They aren't going to be looking at a Roamer. People that want a Roamer, on the other hand, are probably also looking at Hatt 53's, the big plastic Pacemakers, and things like that. They already know they're not buying the most efficient boat, which means that on some level speed is important to them...otherwise they would be looking for a trawler. Your Roamer would essentially be an extremely inefficient trawler, or an extremely slow family cruiser, which would appeal to neither group.

My recommendation (for whatever it's worth), is to size your power appropriately to the boat's intended cruise speed, and then throttle back to 9kts if that's the speed you want to go. You are already going to be about as efficient as you can get if you are putting in new diesels...they've made big improvements over the years with the fuel rail design, etc. The new ones barely even smoke, and are much more economical.

If you want to play with the setup, I would recommend measuring the distance between the top edge of your prop shafts and the bottom of the hull above them. Multiply that by 2, and then size your props as close to that number as you can get while still leaving at least 3" in clearance. Also, play around with the pitch. From an efficiency standpoint, the higher the better. It usually runs less than $200 to have two props repitched, so you have room to play around with this until you find the setup you like.