Cruising speed

Stu Jackson · Oct 16, 2017

What engine? Most likely an M25 XPB. That B is very important, because it is a different engine than an M25, or an M25XP.

Alansails · Oct 16, 2017

As we sail on sweetwater, we do not have barnacle issues or need a diver but the boat should have a hull speed around 6.7 knots and our water temp is always at 160.
Hope this helps. We love our 310!

shemandr · Oct 16, 2017

What about the rest of the bottom? 4.1 isn't very close to hull speed which the 26 hp engine should get you near. There may well be barnacles on the prop OR it could have a very dirty bottom. One often goes with the other. The running hot - it all is consistent.

KZW · Oct 16, 2017

Amazing Grace has the Universal (Westerbeke) M-25 XPBC (C is for Catalina) with a fixed 3-blade 15-9 prop. I normally cruise at 2600 RPM which yields 5.2 to 5.5 knots in flat water. Temperature stabilizes at 175, but then the water is always warm here. At full throttle it will top out above 3,000 RPM.

smokey73 · Oct 16, 2017

Fouling on the prop will decrease the wide open throttle (WOT) rpm dramatically as well as the speed through the water and increase the temperature. The engine just has to work too hard. Other things affect the WOT rpm including the prop size and pitch so every boat may be different. In general you should be able to (and should) cruise at about 75 to 80 % WOT for the best fuel economy and life of your diesel (they don't like to run at low load). Ideally you should be able to get to the rated WOT but that may not be the case with your prop/pitch combination (but you should get close if not you are over-propped.). With the prop clean, the speed you achieve through the water will also be affected by possible hull growth or fouling. Are they diving on the boat and cleaning the bottom too. If the hull is clean, the running gear is clean and the prop is sized correctly, you should get near the diesel rated WOT and the speed that other's get (may or may not be hull speed for your boat, depending on the design).

jviss · Oct 16, 2017

I hate the use of the term WOT, or "wide open throttle" when referring to diesel engines. Diesels don't have throttles. The percentage would be of maximum speed. The speed control on a diesel is just that - a speed control, linked to the governor.

leo310 · Oct 16, 2017

On mine we cruise at 5.5 kts @2200 rpm 3 blade prop but I have a 29hp yanmar in my 310

Ron20324 · Oct 16, 2017

"Diesels don't have throttles" ? My dictionary : "The valve, or it's control lever, or pedal that regulates the fuel vapor entering the engine." Or are you going to nit-pik that, too?

SFS · Oct 16, 2017

It could be worse. One of my flight instructors insisted that I use the term "power levers" rather than throttles.

leo310 · Oct 16, 2017

Now let call it a FCU (Fuel Control Unit) the more you let the fuel flow to the injectors from the FCU the higher the rpm

jviss · Oct 16, 2017

How about "speed control?"

Kings Gambit · Oct 16, 2017

Lisa said:
The only thing standing between us and a 310 is some barnacles, we hope.

Did our see trial on the 310 and the 26hp universal would only top out at about 2600rpm with a speed of about 4.1kts. Engine temp went over 180. Back it down to 2000rpms and she dropped to about 170. The owner said she normally will top out at around 3200rpms and 6.2kts.engine temp runs just below 180.

Said barnacles on the prop causing the problem. They are having a diver come in and scrape the prop. Wondering what everyone else is experiencing with cruising speed, top speed, engine temp and rpms? Trying to get a feel for where we should be when we go back out to confirm.

Thanks

You may be seeing the tip of the proverbial ice berg of problems from a boat that evidently has not been well maintained. Boats that receive regular maintenance rarely have enough barnacle or other fouling on the prop sufficient to cause the problems you are describing, IMHO. There may be other engine maintenance issues responsible for the over-heating. I'd say the sea trial has failed to meet contingencies and move on.

Ralph Johnstone · Oct 16, 2017

Kings Gambit said:
You may be seeing the tip of the proverbial ice berg of problems from a boat that evidently has not been well maintained.

King's Gambit has echoed my thoughts right from the start of your question. Lack of maintenance is a given for this boat as evidenced by the seller's lack of interest in preparing the boat for sale.

You didn't mention a surveyor or did I just overlook it ? I would strongly recommend one in this case as I suspect you may be looking at a boat that could become VERY expensive after you take possession. Hopefully a surveyor can throw more light on this.

smokey73 · Oct 16, 2017

I wouldn't jump on the lack of maintenance just yet. Where is the boat located? How long has it been since it has been sailed, etc.

I take very good care of my boat. Even when I can't go out I try to get by at least once a week to to start the engine and spin the prop and "sling off" growth from the prop and start the generator. I always run both diesels under load (I'm on a mooring) until it is at operating temperature, cool it down and then shut down (same as we did at Nuclear Power Plants). Even then, skipping two weeks, barnacles had grown on the prop and when I went to move the boat from the mooring to a slip to do some work, I could hardly make way against the current here in Beaufort. (we get a lot of growth here) There should be plenty of other indicators if the boat wasn't well taken care of and those along with the prop issue should of course be looked at but I wouldn't assume poor maintenance strictly based on a fouled prop or even a dirty bottom. It may be just that the owner hasn't been able to get to the boat for a period of time for some reason. A good survey along with a thorough sea trial will tell you a great deal about the boat. Your survey should include a haul out for a bottom and running gear inspection too.

leo310 · Oct 16, 2017

You stated you did the sea trial but did you do a haul out if you did what did the bottom and prop look like, if not I hope you have it planed before you hand over the money as you may find that it may need bottom work ie new prop that you can reduce the cost or have the owner do the repairs before any money change hands. As for speed what were you looking at GPS or the ST60.?