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I just got back from the lake doing some more testing on the capabilities of twin 70hp Evinrudes on an Outrage 18. I spent a couple of hours and enjoyed myself knowing that this would probably be my last venture out in the vessel because it is supposed to rain all this coming week and the new owner is going to pick her up next weekend.
Anyway, here is some data that I gathered. All speeds were taken using a GPS.
A. Planing
The boat will plane on one single 70hp engine with the other lifted out of the water.
Top speed on one engine was right at 30mph at max WOT of 5400 rpm.
The manual states 5500 rpm is max for these engines.
The engines have 13 3/4 x 15 pitch props.
Either engine runs approximately the same as stated above.
30mph is not a bad speed with just a single 70hp motor on this vessel.
I was really impressed.
B. Cruising with twins
At 4500 rpm I got a cruise speed of right at 30 mph.
At full throttle, the engines went beyond the max rated rpm of 5500 so I had to back off.
This tells me that when using both engines, the props could be changed to 17 or 19 pitch for better top end speed. The reason the 15 pitch props are on here is probably due to the fact that the former owner used it a lot for water skiiing. So, I can't give you an accurate top end speed with these twins as I didn't want to over rev the engines and keeping them at 5500 rpm would not have given me the true top speed except for these 15 pitch props.
I have heard about prop pitch before on twins. If one engine breaks down, then the good engines prop should be changed to a lesser pitch so it would run near the WOT speed for the trip home. People that own twins recommend carrying such a prop as a spare yet they also mention it is very difficult to change the prop while bouncing around in the ocean hanging off the back of the transom.
C. Hole Shot
The hole shot with the twins was fantastic. Almost immediate.
The hole shot running with only one engine was fairly slow, but once on plane, she went almost as fast as my prior Montauk with a 70hp Evinrude on it. Not bad at all for a single 70hp on this boat. The hole shot also has a lot to due with the 15 pitch prop. I don't think the hole shot would be as good with the 17 or 19 pitch. I know from my experiences with the same engine on a Montauk that the 15 pitch gave a much better hole shot but less top end speed than a 17 pitch.
D. Manuverability
I pulled up next to a buoy and put the starboard engine in reverse and the port engine in forward, turned the wheel to starboard and this thing went in a 360ยบ circle right next to the buoy without moving away from it. She just sat there on the same spot and spun around. Amazing.
E. Trimming
The Tilt & Trim of each engine is almost like having trim tabs. If you want to raise the port side of the boat then lower the port engine a little via the trim button and the port side raises. Same goes for other side or any combination thereof. Another neat thing about twins.
F. Sound of twins
Wow... The sound of twins is really cool. Hard to really describe but they have that harmony between them so to speak as they work in unison.
I know you folks that already own or have owned twins know this but I wanted to post my results here for twins on an Outrage 18.
I will add more information later if I think of anything else.
I stopped the full speed check once I realized that the engines went to 6000 rpm's when they should only go to 5500. Need to try 17 or 19 pitch props so the max rpm's will be within the specified range for these engines. I know I could have taken them up to 5500 to see what they did but didn't think about that as I was more concerned about over reving the engines.
I don't think I will get another chance at this. Maybe the new owner will experiment with the props he needs for his use. The 15 pitch seems to be a great prop for water skiing with this boat as the hole shot if phenominal.
Twins do have twice the drag but they also have two propellers in the water. I was doing 30 mph with just one engine via GPS. With two engines, would it do 60 mph? No, I don't think so but hey, that's what experimenting is all about.
Too bad we don't have everything at our disposal to try out all the different combinations of engines, props, etc....
