2001 SD 310 Cruise Speed

[Northern Ivy]

Greetings, I am interested to see what other 310 owners find to be a comfortable cruise for their 310's? Our has twin 5.7 350 horizons with V-Drives. We just had our props scanned this year and find that with two people full to 3/4 fuel we run 20knts at 3800-3900rpms? Does this sound about right? This is typically in a light chop with a current of some sort. Our Navman fuel monitor tells us that we are burning about 22-24 gallons an hour.

Interestingly enough itt seems that the boat wants to run at between 4000-4100 RPMs and 22-23 knots but I have always worried that this was running the engines to hard.

thanks,

NI

 

[STIHLBOLTS]

Northern, glad to see you on the board. :smt038

 

[Coram Deo]

310 cruising speed

I have the same st up on a 2000 310. WIth 1/2 tank or so of fuel and a family of 5 on board my cruise speeds are approximately the following:
3300 RPM - 3500 RPM 20-23 knots

Your crusising speed seems slow. The above is with a clean bottom. I have seen posts in the past regarding the 310 that had differently pitched props but I cannot remember what they were.

 

[RonF]

Here is my story of different pitched props. You might have seen it back on the SeaRay Owners board.

Original props were 16x17. I am the second owner of the boat. With those props, the boat labored to attain 19 kts at 3400 RPM and toped out at 23 kts at 4000 RPM. In two years of use, nothing in the way of cleaning, loading, trimming, or engine tuning ever helped.

At a time that I was having damaged props serviced, the prop shop said they always recommend 16x15 for a 310 Sundancer. So I bought a new pair, and crossed my fingers. Well, the difference was amazing from the first moment I hit the throttles. These props must match the engine's torque curve better. The boat comfortably accelerates to 20 kts at 3400 RPM cruise, and tops out at 27 kts at 4600 RPM. I've put about 70 hrs on the boat in the year since changing props, and the results are completely consistent.

I was advised not to repitch my old props, so I just had them reconditioned and keep them aboard as "get home" spares. If yours are in good shape, you might just have them repitched.

 

[sbw1]

Greetings, I am interested to see what other 310 owners find to be a comfortable cruise for their 310's? Our has twin 5.7 350 horizons with V-Drives. We just had our props scanned this year and find that with two people full to 3/4 fuel we run 20knts at 3800-3900rpms? Does this sound about right? This is typically in a light chop with a current of some sort. Our Navman fuel monitor tells us that we are burning about 22-24 gallons an hour.

Interestingly enough itt seems that the boat wants to run at between 4000-4100 RPMs and 22-23 knots but I have always worried that this was running the engines to hard.

thanks,


Not sure what the pitch should be for your boat but running your 5.7s at 3800-4100 is way too much. You are overloading them and will shorten their lives at these RPMs.

 

[Chris989]

Ron has it about right. I researched the heck out of prop's on REFLECTION and the 16 X 15's are the way to go. I'm getting about the same RPM / Speed's he indicates. We're cruising 3400-3500 RPM range at about 21 knots.

I originally researched prop sized because at first they seemed a little under-pitched for this boat (not based on performance, just on all of my previous experience) but the lower pitch makes a huge difference in the time to plane, overall speed and load on the engines.

 

[jackson]

310 props

I have a 2002 310 with the 350 Mags/v-drives. I also get about 20-23 knots at 3300-3500 rpms. I believe my props are 17X20, but now I have to doublecheck after seeing the other posts.

 

[jackson]

310 props

Yup, 17X20. It sounds a bit off, but I get good performance. I also checked the prop chart on Searay.com and it was right.

 

[RonF]

Jackson,

If your props are really that big, then I suspect that you have a different (higher?) gear reduction ratio in your transmission. I bet there was a change at some time in the production run.

I remember that my original 16x17 props did match the official SeaRay chart, but I figured that it was some theoretically correct size that they picked without actually trying them out.

Thanks for the additional data.

 

[Coram Deo]

If I remeber correctly my props are also 16X15. I remember checking them during a short haul and cleaning this year. She is out of the water now so the next time I go check on her I will make sure of the size.

 

[Northern Ivy]

Thanks for the feedback....

This scenario is really perplexing to me; last season we had two new long blocks installed (long story and I can not share the details at this time); the bottom was cleaned and the props were scanned and scoped by a prop scan dealer; the props are ISO class 1 exactly at the 17x20X1.5" the specs that sea ray states in the prop sheet. At wide open throttle the boat hits 4800rpm on the money. One interesting point when at WOT my throttle levers are between 3/4 and 5/8s of the way forward (and the port throttle is further forward then starboard). Once the boats hits WOT if you continue to move the throttles all the way forward nothing happens. I am expecting that the throttle lever is a purely mechanical adjustment but I just wanted to share these further details.

Any ideas on what could be the issue? Any suggestions on where to go from here?

 

[jackson]

310

It definitely sounds like you're not getting the speed you should be. What are you reading for top speed at WOT 4800 RPMS? Also, your props are the same as mine. Just curious, is it a 2002? My throttles are also a little off from each other once you get on plane. I don't think any are exactly the same.

 

[Coram Deo]

My 310 is a 2000 and it has different props then High Maintenance. I believe earlier someone mentioned different transmissions in the later boats. This could very well explain why you are getting lower speeds if you have an earlier 310 like mine. I do not get to 4800 rpm's on my boat and my throttles do exactly the same as you describe.
You can see my speeds from an earlier post.
Is the prop chart you are using for the same model year boat you have?

 

[Northern Ivy]

So frustrating

Just to give some further details the 310 is a 2001 and I had referred to the 2001 sea ray prop chart prior to the scan I would have to look but I believe that my gear reduction is 2:1.

Initially when I took the props to Atlantis Propeller; the recommended that the props be tuned to 17X19X1.5". This is what was done; on the initial sea trial it was determined that the props were turning 5200 RPMS at WOT; given the fact that we had just re powered I had the props changed to the exact Sea Ray Specification to ensure the proper WOT.

At WOT with 3/4 fuel and water and two people we saw 27 knots at 4800 RPMs. This was on a dead flat water (15-20')on a very protected river at slack tide.

The problem seems to be once we get in any real water it takes 4000 RPMs to keep 20 knots in calm but more real world conditions. It seems that must people here are cruising at between 3200-3500 RPM; at 3200 I am barely on plane at around 15 knots and 3500 RPM is 16-17 Knots.

I know that this is confusing but any idea that you could provide would be greatly appreciated.

 

[RonF]

NI,

Yes very confusing for your top end to be on spec but cruise to be so far off. I usually cruise with the trim tabs all the way down (rocker switch tops pressed down). Otherwise I might fall off plane in choppy water. Make sure yours are working properly.

You might try using a shop tach on the engines to see if the console tachs are accurate at mid-range.

V-drive boats are already stern-heavy. Make sure you don't have a load of heavy objects in the stern compartments.

I presume you are checking speed with a reliable GPS, didn't you get a new one last year (or do I have you mixed up with someone else)?

 

[Northern Ivy]

Confusing is an understatement

Ron, thanks for the reply. I agree that this scenerio seems to be very odd. Up until very recently I was under the impression that my trim tabs operated in reverese. Meaning that depressing the top of the switch would retract the tabs. I also was under the impression that one should run with as little tab used as possible. Either way; I have ensured that the numbers that I have posted are with the most/least tab for the given scenerio (WOT speed was with the tabs all the way up). I typically watch my speed and fiddle with the tabs to see if I can find an improvement once the boat settles.

As far as weight. We typically run with full fuel (I am anal) and just the wife and I aboard. We have two chartplotters on board and both record the same speed; so I am confident that the speed be recorded is accurate. I do want to check my tachs with the a shop tach (I beleive that this can also be done through the merc tool that is hooked up directly to my horizon engines).

What are the chances that my new long blocks are not producing the appropriate power in the mid range? Of course the engine guy says props and the pro guys says engine. At least in my book the prop guy wins as he can prove his point? What could I look for on the engine side? Everything seems to run fine other then this issue. The long block have a 1 year warranty so I really want to learn of big problems sooner then later.

NI

 

[Coram Deo]

I went back and looked at the prop chart on Searay.com and saw that the props I am running and the recommended props are different. I am getting the cruise speeds I mentioned earlier in this thread with a slightly higher WOT speed around 29 knots. With a clean bottom I actually hot 30 knots WOT this year.
I also noticed that my drive reduction was 1.5x1 and as you said yours is 2x1.
Can you call a local Sea Ray dealer, I know you had issues with the one you originally used, but another one and see what they recommend?
Unless the fuel delivery is off on your boat it would seem odd to have normal WOT and be so far off at cruise speed.
When you bought the new long blocks did they recalibrate your ECM's? When I had new heads put on they had to recal my ECM's to match.

 

[RonF]

NI,

Sorry, I don't know enough about engines to make an educated guess. Our boat had long blocks and revised mufflers installed befor we got it. I assume that the former owner did not notice the RPM issue.

 

[Dave M.]

I think your props are doing what they should be doing at 3500 RPM, considering what your speed is at 4800 RPM. You need to consider what speed the boat would be going at lower engine speeds based on what it does at WOT, or the speed where prop slip is minimum. In your case, it is WOT, which is not uncommon.

To do this, you take known actual speeds at different RPM's and make a plot. This is normally what you might see in a boat test. Then to this plot you add a straight line from 0 RPM and 0 speed to the point where prop slip is minimum, ie 4800. This draws a line that represents the least prop slip your boat is capable of. It does not indicate what that number is, it is just the minimum. Then if you want, and I have done it here, you can add another curve that is 10% slower, representing 10% more prop slip. This second line is not terribly important, but gives you an idea of relative slip.

So then you look at your speed for any given RPM and see how it compares to the minimum slip line. You obviously cannot go faster than the minimum slip line, or you would have to readjust your line. Normally, when a boat is getting on plane, there will be a lot of slip when just coming on plane. As you get more solidly on plane with more RPM, the slip approaches the minimum slip line.

I took the data from your various posts, and made the chart below from your data. This shows that at 4000 RPM, you have almost no additional slip, you are going as fast as you should at that RPM, given the WOT speed. Between 3500 and 4000 the boat is going from a bit over 10% additional slip to nearly none. I think this is very normal, given the boat speed. It is the speed, shape, and weight of the boat, not the RPM, that shapes this curve. If you look at the curve at 3400 RPM, it should be obvious you could not be doing over about 19 knots, and probably just hanging on to plane. And when you get a little wave action, it will drag you down more.

What I see is that at 22-23 knots your boat is solidly on plane. Explains why it feels like it wants to run there. Mine needs 30 MPH to do the same.

So, I think if you want the performance you expect at 3500 RPM, you have to determine why your WOT speed is 27 knots. That is the real problem. I am wondering if you have an RPM limiter that you are hitting, and that you are under propped and don't know it. Coram Deo suggests this, and the possible cause. Note that he is propped so that he does not get to 4800.

Here is data that I picked out of the posts. I did not know just what RPM CD got for WOT, so assumed 4600. I also put his two numbers for cruise speed as separate entries.

And here is the chart of the data above. I don't think CD really intended the two sets of numbers he presented at cruise as individually accurate, but rather as a range. I put them in individually anyway. They do suggest, if accurate, that his boat is also seeing the slip increase, as speed drops below 22 knots.

And here is my boat, with little fuel and full fuel on board. It has minimum prop slip at about 3600 RPM, and 31 MPH. It is really on a steep slope, trying to fall off plane, below 3200.