1984 Outrage V-20 Re-power

[MikeUFCfan]

I have a 1984 OUTRAGE V-20 powered by a YAMAHA 250-HP Ox66 two-stroke-power-cycle engine. A Mercury 8-HP auxiliary engine is also on the transom. I live in the San Francisco Bay area, and I really do not need a V-20 that can to over 55-MPH. If my boat speed maximum was around 35-MPH I would be happy. I want to re-power and am unsure what engine to choose.

My main concerns for the re-power are improved fuel efficiency and thus increased range. To reach bluefin tuna, I have to go 30 to 40-miles offshore. I do not feel comfortable running out that far and then spending hours trolling at a speed 10-nautical-mile-per-hour or faster. To feel safe I would bring an addition 10 to 20-gallons of fuel in jerry cans.

I am considering buying a used Yamaha 150-HP engine (perhaps means F150), but I also think a 115-HP engine might be all the boat needs.

Also, a SUZUKI DF140. engine would be great for re-powering the OUTRAGE V-20--from what I have been told.

Q1: for the use described above, what engine would be recommended for re-powering my 1985 OUTRAGE V-20?

Q2: what fuel efficiency in statue-miles-per-gallon can I expect to get with a modern engine at a boat speed of 25 to 30-MPH



ASIDE: Hi all. I know there are plenty of conversations about re-powering these classic whalers, but I wanted to give my situation and pick some brains.

[jimh]

I have a 1984 OUTRAGE V-20 powered by a YAMAHA 250-HP Ox66 two-stroke-power-cycle engine.

My first thought on reading that sentence is your OUTRAGE V-20 must be a rocket ship. That hull is easily driven on plane, and with that much horsepower I would worry about the stability at full throttle boat speeds. These classic Boston Whaler hulls were not really designed for much more than 50-MPH top speed, if that.

To assess how much power you need to maintain a a cruising speed of 25 to 30-MPH (and here I am working in statute miles, not nautical miles) I will use the Crouch Planing Hull Speed prediction formula. First, I will use your data to figure out an approximate boat weight. Here I assume with 250-HP the boat can reach 57-MPH, and the hull coefficient is 190 (based on some experience with Boston Whaler hulls). The calculated weight is about 2800-lbs. Assuming the re-power engine weight is not much different than the Ox66 engine, to get to 30-MPH the calculated power is then 70-HP.

Continuing on this basis, the 150-HP engine would provide you plenty of reserve power. And so would a SUZUKI DF140. Even a 115-HP would give some extra reserve power.

As for fuel economy, modern engines are somewhat better than the classic two-stroke engines, but the Ox66 engine was perhaps one of the best of breed with regard to fuel economy because of its sophisticated fuel metering system. Because of that I don't expect there will be a huge improvement in fuel efficiency at higher-throttle settings, as would be used when on plane at 30-MPH, so I will estimate the fuel burn rate as HP/11 = GPH.

Now we look at 70-HP for cruise, so fuel burn rate is 6.4-GPH. That gives fuel economy of about 4.7-MPG, which may be a bit optimistic. For an 80-mile round trip, only 17-gallons will be needed.

Those are all best case. If you have to run into rough seas the usual effect is the MPG drops significantly, may be down to 2-MPG or less, so that 80-mile trip might need 40-gallons of fuel.

You have not mentioned the fuel tank capacity on YOUR boat, but the OEM fuel tank for a V-20 was specified at 63 or 65-gallons, so let's say 58-gallons usable. That give you a fuel endurance of nine hours. If you are going 30-MPH, you should have a range of about 270-miles at optimum. Lets be conservative and call it 240-miles (statute miles).

As for the 8-HP auxiliary engine, I will guess you need all 8-HP and its fuel rate is HP/10 for 0.8-GPH trolling. So ten hours of trolling will consume 8-gallons.

[jimh]

As for what engine to recommend, if you want best reliability and best fuel economy, probably the SUZUKI DF115 is a good choice, and it will be less expensive than a 140-HP or 150-HP model.

A good friend happens to have an OUTRAGE V-20 with a SUZUKI DF115, and it can certainly cruise at 25 to 30-MPH with ease, even though he carries a lot of extra weight in fishing gear and downriggers.

On the other hand, if you ever decide to sell the boat, having a 140-HP or 150-HP might make the boat and engine combination more attractive to a buyer who wants to be able run faster than possible with just the 115-HP.

[RodneyBD]

A 115 would likely be sufficient for inshore and bay angling, but for heading offshore with full tanks, ice, extra fuel, people and gear I would want a 150, minimum. My concern wouldn't be top end speed, but for torque when you run into rough weather. You'll want that midrange power available with big head way swells, and for adjusting the throttle when steering through heavy chop as well as down wind seas.