Bayfield 25 - slow under motor

[William Cooper]

I have a Bayfield 25 that's running a bit slow under motor. I can only get up to 2.5 kn - the hull speed is just over 5.5 kn. No known or observable issues with the inboard diesel engine.

I've got a Yanmar YSE8 inboard Diesel engine in the boat - 8hp/3200 RPM.

I do not know the size of the prop - have attached a pic of the prop that's currently on the boat (installed by previous owners).

Any thoughts on why I'm running slow?

 

[kloudie1]

Welcome to the forum, William.. Could be a bazillion things..
First, ya need to get a good RPM reading from the engine when at full throttle and 2.5 kt.. make sure the 2.5 is a good number too; a gps number corrected for any current where you are measuring.... Yanmar tachometers are notoriously inaccurate.. A laser hand-held (https://www.amazon.com/Digital-Phot...d=1505355581&sr=8-3&keywords=laser+tachometer ) is cheap and accurate enough..
The engine should get to 3200-3400 RPM in neutral at full throttle.. If not, start with fuel.. change filters and bleed carefully to get all the air out of the injection system.. make sure there are no fuel leaks .. If you are not comfortable with understanding the diesel, bribe a gear head friend with a couple of beers to get him to help and show you how the thing works.. Get a good shop manual so that you'll have the correct info..

 

[njlarry]

Also check rpm of shaft as a slipping clutch plate is a possibility.
Good luck and let us know how you make out.

 

[jssailem]

Welcome William. Kloudie has you started on the right track.
Max design hull speed for your boat is 5.8 to 5.9

From there it is all down hill depending on hull growth, prop, things dragging in the water, your engine, pushing the boat up current or into the wind.

How were measuring the speed? A GPS showing speed over ground or a knot meter showing speed of water passing the hull?

 

[Benny17441]

I suspect the posted picture may not be current. What is the condition of the hull bottom? Marine growth will impart drag and reduce speed. When was the bottom last cleaned? Growth can develop in a matter of a couple of weeks. The shown prop is no OEM but chances are its size and pitch are not the cause of such significant loss of speed. Like Kloudie indicates check engine RPM and verify the method being used to measure speed. A GPS will provide speed over land and to properly calculate boat speed two runs should be made in opposite 180 degrees course to average out the effects of wind and currents. A knot meter measures speed over the water but they are notoriously unreliable because of fouling.

 

[William Cooper]

Hi All,

Many thanks for the insights. Sharing a few more details to answer several of the questions above.

Speed was measured with a GPS. I was fighting current, but, as suggested above, I took a second speed reading in a direction 180 degrees from the first reading. And no wind to account for.

The prior owner cleaned the hull back in June (have receipts) but I don't think it was ever sailed (could be growth on the hull).

Sounds like I need to get an rpm reading and possibly take a look at fuel filters and bleed the fuel lines. And maybe pull the boat and clean the bottom.

Any additional input is much appreciated!

Thanks all!

 

[jssailem]

William. You might consider getting a diver to clean the bottom. Lot cheaper than hauling and cleaning. Your marina may not permit divers. So either check or if challenged ask forgiveness.

 

[William Cooper]

Thanks again all!

I'll have to check on whether my marina permits divers.

Also, I should have mentioned re: two speed reading. With the current (and very light tailwind), I was only able to get up to 3.0 kt.

Spending the weekend troubleshooting. More to come!

 

[Benny17441]

The boat has an average handicap of 261 and the hull speed is 5.94 knots. What kind of speeds are you getting under sail? Just trying to narrow down if it is the engine or a fouled bottom. It will not hurt to change the fuel filters and make sure the engine is reving up to maximum rated RPM. I don't know how warm the waters get in your area but here in Florida we have bottom sea growth in two weeks and clean the bottom at least once a month. Depending on the condition of the bottom paint you may get more or less growth. Our boat has never gone faster than just after a bottom paint job.

 

[William Cooper]

The same day I took speed readings, I got her up to 5.2 knots under sail.

 

[jssailem]

William, "5.2 knots under sail" That is helpful. But we need perspective. What was the wind speed? Doing 5.2 in 10 knots or 20 knots of wind is different.

Seeing your in DC... Was Congress in session. You know they call Chicago the Windy City... DC has the same affect.

 

[Benny17441]

As you had reported light winds the same day that you took the speed readings it may seem the focus can shift to the engine and prop. Like I suggested before replace the fuel filters and drain the water separator, Observe running temperature and signs of any smoking. You may also adjust the valves gap. Make sure there is no blockage in the intake tube and watch the strength of the water flowing out of the exhaust discharge port. In old engines the grade of oil used can have a direct relationship with compression. The quality of the fuel is also a factor. Lastly a three blade prop imparts quite a bit of drag so 5.2 knots might be as good as it gets under sail. first get the engine to deliver its maximum rated RPM in neutral and then compare to the maximum RPM attained with the propeller engaged and underway. A high pitch prop may not allow the engine to develop maximum RPM while a low pitch one may cause the engine to overrev. Go ahead and also have the bottom cleaned to reduce as much drag as possible.