How Fast Does Your Boat Motor?

[TooCoys]

I asked this on SailboatOwners, but thought I'd post here as well.

I've got a 1980 27' with a Yanmar 1gm10 in it, and it motors extremely slow.

We took it out yesterday for its first test sail since I bought it, and we were being passed by other sail boats left and right. It took us a good 30 minutes to go maybe 1nm?!?

I know that my cutless bearing is loose and will need to be replaced, which I plan on doing next month, but what else could be causing this?

Could the prop be slipping? At one point we though we were dragging bottom because we could hear and feel some vibration, but we were in at least 10 feet of water and I only draft 4.3'. We determined that the prop was turning because of the current as we down wave since the wind was behind us. Is that normal?

People keep telling me that sailing is just slow and that I am just not used to it, but when other boats my size are passing me, I'm starting to get concerned.

How fast does your boat go under motor?

[skipmac]

First you need to determine your actual speed through the water. Does the boat have a working knotmeter? If so, what does it show?

If not, do you have a GPS that will show speed? Go out at slack water or in an area with no current and test your speed.

Once you know how fast you are actually going instead of subjectively that will help diagnose the problem.

MEANWHILE, have you looked at the prop? Is it clean. Just a little bit of growth and fouling on the prop will slow you down a LOT!.

[TooCoys]

Originally Posted by skipmac

First you need to determine your actual speed through the water. Does the boat have a working knotmeter? If so, what does it show?

If not, do you have a GPS that will show speed? Go out at slack water or in an area with no current and test your speed.

Once you know how fast you are actually going instead of subjectively that will help diagnose the problem.

MEANWHILE, have you looked at the prop? Is it clean. Just a little bit of growth and fouling on the prop will slow you down a LOT!.

I had it scraped when it was quick hauled.

[44'cruisingcat]

2 knots - something isn't right. I see the prop was clean enough, but how long ago?

Barnacles can make a prop pretty much useless in fairly short time, if your antifoul has failed.

[TooCoys]

Originally Posted by 44'cruisingcat

2 knots - something isn't right. I see the prop was clean enough, but how long ago?

Barnacles can make a prop pretty much useless in fairly short time, if your antifoul has failed.

The prop was just scraped when I hauled it out two weeks ago. This is what it looked like before.

I know sailboats are slow, but when I'm being passed by other boats my size, its starting to concern me. I know the engine is fine because it runs without missing a beat, but its almost like the prop isn't turning like it should be. Almost like its slipping.

Should I be able to get 5 knots out of an 8hp engine on a 7000lb boat? Could it be that I'm underpowered?

[MarkSF]

"We determined that the prop was turning because of the current as we down wave since the wind was behind us. Is that normal?"

This sentence makes no sense.

[TooCoys]

Originally Posted by MarkSF

"We determined that the prop was turning because of the current as we down wave since the wind was behind us. Is that normal?"

This sentence makes no sense.

Sorry for the typo.

So the boat was in neutral. We turned the boat to head back to the marina, so we were down wind. The waves were rolling in behind us, stern to bow. Either the waves, or the current in the channel under us, we THOUGHT were causing the prop to turn.

Originally we thought we were scraping the bottom but we were in at least 10 feet of water, and inside the channel we were in 14 feet or greater.

[MarkSF]

Why would the current make the prop turn? The boat moves with the current.

Also, Without knowledge of the current at the time, no conclusion can be drawn about your speed through the water.

[TooCoys]

Originally Posted by MarkSF

Why would the current make the prop turn? The boat moves with the current.

Also, Without knowledge of the current at the time, no conclusion can be drawn about your speed through the water.

I don't know, that's why I'm seeking information.

Would a loose cutlass bearing allow the prop to turn? Does the prop normally turn when its in neutral? If the prop wasn't turning, the engine was not on, and we were not dragging bottom, what else could have been causing the vibrations that we felt?

[Excalibur5]

Our first boat was an albin vega (27' with 8' beam) with the same engine you have. I will note it did have a 3-blade prop which generally is a touch more efficient under power.

The 1GM pushed her to around 5.5 knots in still, calm, water when the engine was at about 1900-2000 rpm. Wide open was a little over 6 knots at around 2300 rpm as the prop was pitched a bit steep. With the currents here, that could easily equate to 3 knots at times when bucking current, or around 1.5 knots when pushing into a steep chop.

I will note we got outrun under power by most things out there, and if we had kept the boat, I would have liked to increase the engine size to 16-20 hp. I would guess your hunter is wider than our vega, so is certainly underpowered by at least a bit. That being said, they are called sailboats for a reason. It helps to realize with a sailboat - the journey IS the destination.

What RPM is your engine running at cruising speed? Wide open throttle should be approximately 2400-2600rpm if your prop is pitched right.

Bottom growth (even slime) and growth on the prop can easily cost you a knot or two, so a clean hull is very important.

Also to answer your question - vibration can be caused by a bunch of things. To name a few: misfiring engine, worn engine mounts, engine out of alignment, bent prop or shaft, or growth on prop.

And to answer another, if the boat is coasting in forward with the transmission in neutral, it is normal for the prop shaft to turn. Yanmar recommends putting the gear in reverse while sailing to help prevent undue wear to the transmission. This will stop the prop spinning, but will cause a slight amount of extra drag.

[MarkSF]

For the prop to turn in neutral, the boat has to be moving relative to the water - i.e., being driven by the sails. This would be normal.

When you were going downwind, were the sails up?

What isn't normal is to get vibration when the prop is turning.

[newhaul]

Ok first off this is a wag . Looking at the after pictures it appears that the shaft may be a bit bent look between the cutless and the shaft zincs. Next yes the prop may rotate some when in neutral and sailing.
Next your clean prop is still rather dirty with a few barnacles . I also see what appears to be significant dezincification pitting . Thirdly where is the prop nut zinc.
When you replace the cutless It may be a vood idea to look at changing.the prop to a new or at'm least in better shape properly sized and pitched 3 blade prop.

[TooCoys]

Originally Posted by Excalibur5

. Yanmar recommends putting the gear in reverse while sailing to help prevent undue wear to the transmission. This will stop the prop spinning, but will cause a slight amount of extra drag.

THAT is good information! Never heard that before. Thanks!

[TooCoys]

Originally Posted by MarkSF

For the prop to turn in neutral, the boat has to be moving relative to the water - i.e., being driven by the sails. This would be normal.

When you were going downwind, were the sails up?

What isn't normal is to get vibration when the prop is turning.

Yes. The wind was coming from about our 7 o'clock position, so broad reach I guess?

[Excalibur5]

No problem. It should go without saying, shut the engine off first or you will sail REALLY slow this way!