Speed over ground and trim tabs

[mjohnh]

I have had my 28 TE for 10 months. I have a Raymarine navigation package. We were on Lake Michigan two days ago and I was running at 2000 rpm and my s.o.g. was about 8.1 kts. It has a 315 Yanmar diesel. I used the trim tabs. I have a few questions.

1. How do you know when to apply the trim tabs and when you have enough trim tab applied?
2. I thought that cruising speed on this boat was about 12 to 13 kts. I was concerned that 2000 rpm was only producing 8 kts.
3. I thought that max speed is about 26 its, but am reluctant to crank it up much past 2000 rpm........what is the reasonable rpm operating range of this engine on this boat? I have only 476 hours on it and it is a 2005 model.

Thanks for any input.....

[carolmarie]

My guess is that your engine nameplate will indicate a continious speed of 3600RPM and a max speed (and output) at 3800RPM. A cruise RPM of 2600 to 2800 should yield a speed of 12 to 14 knots. The engine should (would) be "loafing" at a cruise speed of 2000RPM. Don.

[carolmarie]

PS to my post above : re the trim tabs. I simply run up the the approx. speed over ground I want then adjust the tabs to attain a comfortable attitude. Once this done I usually pick up a knot or so in additional speed. Don.

[Tree]

You are running the engine way too slow. You'll do more damage to the engine that way then running at 3600 rpm. Most of us find that the sweet spot with the Yanmar is 3300-3400 rpm. That will give you between 16-18 knots on the standard transmission.

[special k]

You are running the engine way too slow. You'll do more damage to the engine that way then running at 3600 rpm. Most of us find that the sweet spot with the Yanmar is 3300-3400 rpm. That will give you between 16-18 knots on the standard transmission.

X2

[mjohnh]

Tree and Special K: when you say "damage" what do you have in mind? I use the boat for trolling at a very slow speed.....2 kts or so....If you are referring carbon build up...or whatever....would periodic running at the 3400 rpm range reverse whatever "damage" you refer to?

Thanks again

[Tree]

If you were using the boat most of the time without working the engine at around the 2000 rpm mark then you do risk the chance of honing the bores. Do you have a trolling valve fitted? I'll explain the principles of under working the engine when I'm at a PC and not on a smart phone.

[Tree]

Here is a link, pay particular attention to the last paragraph with regards to a high speed diesel.

http://www.marinediesels.info/2_stroke_ ... eaming.htm

Now i will try to explain this the best i can using two engines.

Engine A is for example your yanmar and has a cylinder length of 5"

Engine B is for example a Cummins 370 and has a cylinder length of 10"

For engine A to reach the top of the cylinder, it takes 1 second, engine B takes 2 seconds. As a result the crank on engine B rotates slower than that of engine A. In order for engine A to have the same piston speed in the cylinder it needs to travel at twice the speed of engine B, resulting in the output from the crank to be twice that of engine B.

Still following?

So lets say engine B piston speed is X and Engine A is X. If engine A has half of the distance to travel then it would have a stroke time of 2X versus 1X of Engine B. If you were to reduce the output speed of Engine A by half to match that of Engine B, Piston speed would then become 1/2X which could lead to some of the issues listed in the article previously mentioned. Not the easiest of things to explain by typing on a forum but hopefully it makes some sense?

In a nutshell, an engine running at 4000 rpm at the crank with a cylinder length half of that of an engine with a 2000 rpm output at the crank would mean that the pistons inside the cylinder are both moving at the same speed. It is just the crank output that is faster and the result is wear on the engine should be about the same.

One other thing that is worth noting with the Yanmar engine is not to run it at the same speed all the time - High speed engines need to be run through the rev range to maintain longevity. Also try not to idle the engine, when you start for the day wait till the last minute and try to get some load on the engine a few minutes after starting. These engines are designed to be used, don't be afraid to open up the throttle and give them a good thrashing once in a while.

[mjohnh]

Tree: Just to make certain that I understand your example.......would not the crank wear and valve wear be greater on Engine A compared to Engine B (referring to the next to last Par).........I appreciate your input.........

On another subject, but I think that you know your "bangers" sort of speak......is there an easy way to know or check if the timing belt has been changed..? My 28TE is a 2005 model.......I am the third owner and took it last August.....it has 477 hours, only. I think that the belt is supposed to be changed every 1000 hours; or, 5 years, which ever happens first. I have not checked the manual, but that is what I read on some post....

Have a great day, mate!!! ps...my youngest son spent a year at Warwick College and loved it.....not near you, but a great maths program.

[Tree]

You may get more wear in the crank area, but those area are relatively easier repairs to make than having to rebuild the entire engine. I'd guess that Yanmar, Volvo etc took this on board when developing the high speed engines we all know about today and have developed harder wearing materials to take this into account.

With regards to the timing belt, the only way to know is documentation. An engine with a 1000 hours on could have a timing belt that looks like it's fresh from the box. For peace of mind I would change it on the next service. Engine box model or flush deck?

[mjohnh]

Engine box model.

[Tree]

Ok it's a bit more difficult to access the cambelt but it is doable. Might be worth asking on the forums if there is a mechanic in your area that anyone can recommend

[special k]

regarding timing belt question my certified yanmar guys placed a metallic sticker on top of timing cover with date and hours.

engine box model all done without lifting motor

[Halcyon]

Mechanics frequently write on the harmonic balancer so the know which piston is up.

When i had mine done at 600h the mechanic said it had been done before judging by the marks. no decal though.

[mjohnh]

Thanks....I will look for some indication of prior work on the timing belt.....