310 Sundancer - RPMs, Crusing speed, Etc.

I

island time

New Member
May 20, 2007
7
Hi all.

I can't find any good performance data on my 2000 310DA. I can find data on newer models, but no test results on my year. Maybe they are the same, but would like some input.

350 MAG MPIs
V-Drives
Not sure of props, but I do recall they are the factory recommended.


Looking for speed and MPG at various RPMs.

And specifically, is 4000 RPM too hot to run at? The data that I have seen on newer DAs shows that 4000 is the best efficiency, but that just seems hot to run at. I have been cruising at ~3400 but I have a big trip coming up and want to minimize time and balance it against gas-money as best as I can.

Thanks all.
Dave
 
310

I think I get the best ride, fuel burn, etc. at 3400 RPM. At this RPM I get about 20 mph/23 knots with 350 MAGs/v-drives. On long runs at this speed I burn about 20gph every time.

I usually don't push it any harder than 3600. I think I went 4000 once and I forget the speed. Not sure of the performance data at this RPM, but it feels like it is pushing too hard.
 
310 Best RPM

I ran a 310 DA 800 miles up the ICW. I agree with Jackson, the best RPM to run those engines is approx. 3400.

Mark
 
Dave,

1999 310 DA, 350 Mag MPI V drives.

I cruise at 3400 RPM and about 20 Kts on the GPS. Good handling and comfortable ride up to about 4 ft chop. Below 3200 RPM I fall off plane, and the boat drags down to about 15 Kts. I don't know the GPH at 3400, but 20 sounds right.

I have not spent any time at 4000. The motors top out at 4600 RPM and about 25 Kts. I don't do this for long, mostly just to make sure that everything is running OK.

I am the second owner. I changed props because the motors were over-propped from the factory.
 
310

RonF is correct about the maximum knots. I had my mph/knots conversion screwed up, but I do get 20 mph at 3400.
 
Any advice would depend on similar setup - including props. So first, you should take a run at WOT and see what it revs to. I don't know what the recommended spec is for that engine, but if you're not there you need to change props first. Simply running at a given rpm with the incorrect props would be meaningless.

Aren't the 350 Mag MPI engines speced to 300 HP at 5200 rpm?
Not like my 350 carb engine at 260 HP and 4200-4600 rpm.
 
My 2000 340 DA engine is rated for 3800 RPMs as the top cruising range. I like to cruise at 3300-3600 for speed in the 22-25 knot range, depending on load and sea conditions. 4000 RPMs is too fast for sustained cruising.
 
Thanks all. You all have confirmed my gut instinct at ~3400 rpms.

FYI - props are HyTorq 16x15 3-blade.

On calm to moderate seas I average about 25-26 mph and I am burning just about 1mpg. Right in the range of most of the responses.

Also, these are rated at 300HP, but I do not know at what RPM that rating applies.

Dave
 
The maximum RPM is 4400-4800 according to my Mercruiser manual!
 
RonF, do you know what size props were on the boat before you replaced them and what performance (RPM Knots) you were experiancing?

I recently purchased a 1999 310, new engines (per recall, less than 200 hrs) and the props are Dimex 16 x 15.5. The Starboard prop is bronz and had some cavitation wear which was repaired but needs replacing. The problem is I cannot find a replacement of the same brand / size.

The only suggestion locally is to replace both with 16 x 15. Currently I am getting 20 Knots @ 3200 - 3400 RPM, and WOT @ 4200 - 4400 RPM per survey.
 
Giddy Up,

I currently run about 23 knots at 3200 - 3400 RPMs. That is fully loaded with fuel, water etc......

I'm not sure about the prop size but I may call Sea Ray as I know my props have not been replaced.

I am also curious with regard to your engines replacement due to a recall. Do you or anyone else out there have additional information. Although I have not have problems, it would be good to know about! Thanks!
 
310

correction on my speed - I cruise at 23 knots/25 mph at 3400 rpm, not 20 mph as I stated before. I realized my tridata is off and I just made a 2 hour run at this speed. My props are 20X17.
 
Giddy Up said:
RonF, do you know what size props were on the boat before you replaced them and what performance (RPM Knots) you were experiancing?

I recently purchased a 1999 310, new engines (per recall, less than 200 hrs) and the props are Dimex 16 x 15.5. The Starboard prop is bronz and had some cavitation wear which was repaired but needs replacing. The problem is I cannot find a replacement of the same brand / size.

The only suggestion locally is to replace both with 16 x 15. Currently I am getting 20 Knots @ 3200 - 3400 RPM, and WOT @ 4200 - 4400 RPM per survey.
Click to expand...

Sorry for delay, on vacation, so web access is spotty. This boat had the engines & exhaust replaced just 55 hrs before I bought it. It had 16x17 props. I guess the previous owner was satisfied with lower speeds. WOT was 4000 RPM and around 23 kts. Cruise was 3400 and 19 kts. Acceleration was labored. I damaged them in the shallows, and the prop shop recommended 16x15. They seemed to be familiar with Sea Ray overpropping this boat. Yours does not sound overpropped, but I don't think you have originals.
 
Thanks Ron, sounds like I'll have to go with the 16 x 15 as a replacement.

Given your performance it should work well, may turn a little more RPM but would rather that than be under powered.

Thanks again
 
Our 340 with twin 8.1S cruises at 3200 to 3600 rpm between 24 and 31 mph depending on load.

My personal optimal cruising rpm range is no less than 3400 rpm and no more than 3600 rpm, maybe 3800 rpm for shorter times.

Min planing speed is 20 mph at around 3000 rpm, but you're just barely hanging in there and need lotsa tabs. No fun place to be.

Below 3200 rpm the hull begins rise the bow and run rather inefficient without a lot of tabs.

3400 rpm gives you 26.5 to 28 mph and is also good, but you do need some tabs to run optimal efficiency = max. speed at that rpm.

Our 340 really runs best and has a definite sweet spot running without tabs at 29 - 31 mph right at 3600 rpm. It's a sustainable rpm and good speed all around for the vessel.

3800 still sounds and feels comfortable, but this is high enough in the 8.1s engine rpm range for me not to want to be there too long. Speed at 3800 rpm is 31.5 to 33.5 mph

4000 rpm and above gets uncomfortable as the engines are being strained and it shows. I hardly ever hit 4000 rpm or above and if only for brief periods to get in or out of a situation with traffic. You run somewhere around 35 mph, but I have never watched speed closely at this rpm range.

WOT on our 340 is 4800 rpm and 40.5 mph and something I have done only a couple of times for about a few minutes. Things are loud and vibrations are setting in that rattle the cockpit cabinets. An entirely uncomfortable place to run this boat for any amount of time.

All speeds are GPS SOG.
I have the standard 340 issue Hurth 63V 2.00:1 trannies and 3-blade 18x22x1.5 3BMC Nibral props and a clean hull.
 
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