Propeller advise?

[McIntoshUSA]

I'm still a newbie. Bought my first sailboat in April 2014. My new to me boat came with a Campbell Sailor Propeller. http://www.westbynorth.com/CampbellSailer.aspx
The previous owner talked like it was a really good prop. I know nothing about props. Since buying the boat and sailing it, I have wondered if it is a good prop or not? My 30' sailboat only has a Universal 14 HP (2 cylinder) diesel engine. She cruises under power at 3/4 throttle at about 4-5 knots depending on current.

I have read about folding props and feathering props. I realize that I would have less drag when sailing with a folding or feathering prop, but I am curious if I would gain any speed when motoring. I am concerned that when motoring with other cruisers that I might not be able to keep up with them. So my question is would I actually gain any speed when motoring with a folding or feathering prop? Is there a big difference between a 2 blade and 3 blade feathering or folding prop?

Thanks

 

[31seahorse]

My 30' sailboat only has a Universal 14 HP (2 cylinder) diesel engine. She cruises under power at 3/4 throttle at about 4-5 knots depending on current.

So my question is would I actually gain any speed when motoring with a folding or feathering prop? Is there a big difference between a 2 blade and 3 blade feathering or folding prop?

Thanks[/quote]

Hello McIntochUSA, The speed you get motoring seems OK to me. At 3/4 throttle there would be a little extra left if you needed to push through headwind, current, or other action. We have a Martec two blade folding prop on our 28 Caliber. The boat moves forward very well, but reverse is a direction that requires some getting used to! With fixed blade, two blade props I was always confident in my ability to back the boats under control to where ever I wanted them. With the Martec folding prop I must be sure to come to a complete stop before shifting to reverse and I must always account for prop walk to the port side as I begin to move backward. The cost of a folding prop far outweighs any increase in sailing speed that I ever experienced. Both Martec props we ever used were already on the sailboats we bought. I did have our current Martec refurbished by the company and it works better than it did prior to repair. 31seahorse

Give a look to the zinc if that is a current photo.

 

[capta]

That looks like a very inefficient prop, but also low drag, which is probably the idea. I'm not too sure why you are so concerned with keeping up with other boats when you are under power, but the prop is only one factor involved.
How clean the bottom and prop are, is a much more important factor than the actual prop efficiency. Also wind and sea conditions will alter your speed under power from one outing to another.
We love our Maxprop, but do you really think it's worth that kind of investment on your first, learner boat?

 

[Sprega]

You have a very nice prop. Low drag and efficient motoring. If I could afford it, I would chose the same one.

 

[MSter]

Can you get to your engines max rpm with that prop? If you can get 95% of max rpm then prop is likely proper size. You should be able to get to hull speed without to much exhaust smoke . Lots to learn !
Mike

 

[McIntoshUSA]

Can you get to your engines max rpm with that prop? If you can get 95% of max rpm then prop is likely proper size. You should be able to get to hull speed without to much exhaust smoke . Lots to learn !
Mike

How do i know what Max speed should be?

Thanks

 

[seadaddler]

Prop$$$$$

Adding any kind of folding prop will be $$$$$$ and you may be
very unhappy $$$$$ and not see a big difference after spending $$$$.
You are new and so first use the boat for the first year and make sure the
hull and Prop is clean and everything else is good fuel filters.
What you have as a prop is very well rated and sounds like your boat is doing
good speed wise and wait after the first year and see what really needs work.
Nick

 

[Deleted member 117556]

I just went through an evaluation of my prop and can share with you what I learned. My engine is undersized, ie: yanmar 2gm20f which is 18 HP for a Catalina 310 with almost 11,000 lb displacement. I worked with a yanmar expert and did the following:
1. Is tachometer accurate? Used a handheld device to verify that. Check
2. Does engine reach max rpm out of gear? For my engine that is 3,800 rpm. Check
3. Does engine make maximum rpm while in gear (away from dock)? For my engine that is 3,600 rpm. Mine hit 3,510 rpm (measured) at full throttle. This is almost perfect according to yanmar expert.

So my conclusion is that the 4 blade, fixed 14" prop is ideal. Still only make about 5.5 knots under power at 3,000 rpm. Cleanliness of bottom, shaft and prop is also a big contributor.

Hope that helps.
bob

 

[woodster]

Adding any kind of folding prop will be $$$$$$ and you may be
very unhappy $$$$$ and not see a big difference after spending $$$$.
You are new and so first use the boat for the first year and make sure the
hull and Prop is clean and everything else is good fuel filters.
What you have as a prop is very well rated and sounds like your boat is doing
good speed wise and wait after the first year and see what really needs work.
Nick

that is very good advice Nick

 

[McIntoshUSA]

Thank you everyone for your help. I believe I will keep what I have. I guess I will clean the hull again. I did notice a little speed increase last time I cleaned it. It looks clean but I guess looks can be deceiving.

Thanks

 

[FastOlson]

How do i know what Max speed should be?

Thanks

While the hp of your diesel may be a bit lower than optimal, I would estimate that your size boat should motor at 6 kts all day long. Or faster.

This presumes that the bottom is clean and smooth. Your particular prop is, as others note, a compromise between drag under sail and blade area under power. I have looked at one of those and it looked really inefficient to me, but I am no engineer.

Our boat does not compare directly with yours, but it did take me over a decade to figure out the best pitch for a newer three-blade fixed prop. I also had that prop trued up and balanced by a "prop scan" shop in my area (it was out of balance from the factory; it's a Michigan, if you're curious). For 15 years we thought our boat was good for about 6.5 under power.... nowadays we motor at 7.0 any time at the manufacturer's recommended rpm (2500 for our M25XP). Consult your engine manual for this information.

Best of luck,
Loren

 

[Ken Cross]

You asked about your hull speed
Here is a great link:
http://tomdove.com/sailcalc/sailcalc.html
Select your boat and anything else then hit "Make Chart"
It says your hull speed is 6.9 knots

KEn

 

[Ron20324]

...2. Does engine reach max rpm out of gear? For my engine that is 3,800 rpm. Check
3. Does engine make maximum rpm while in gear (away from dock)? For my engine that is 3,600 rpm. Mine hit 3,510 rpm (measured) at full throttle. This is almost perfect according to yanmar expert....

Convention has it if you can hit 3800 in neutral, you should be able to hit it in gear. IIRC, Your "almost perfect" seems 300 off, which is maybe an inch of pitch.

 

[McIntoshUSA]

You asked about your hull speed
Here is a great link:
http://tomdove.com/sailcalc/sailcalc.html
Select your boat and anything else then hit "Make Chart"
It says your hull speed is 6.9 knots

KEn

Thanks Ken

Great website.

 

[FastOlson]

You asked about your hull speed
Here is a great link:
http://tomdove.com/sailcalc/sailcalc.html
Select your boat and anything else then hit "Make Chart"
It says your hull speed is 6.9 knots

KEn

One caveat: all the calculations - web or printed book - will have one facet missing from their data. That's the difference in DWL and actual sailing or motoring WL.
If you have a hull design with a lot of slope or "tuck up" to the stern profile, there's not much difference in WL length between being at rest or being under way.
A lot of modern hulls will have a much straighter run to the bottom aft, and this will add as much as several feet to the hull in contact with the water once you get over 3 or 4 kts.
On our particular model, the static (measured) WL is about 28 feet. Moving along at 6 kts we are at about 30 or 31 feet. That's why we can motor at 7 kts at cruising rpm with the diesel. I would note that we are NOT an ultralight boat. Brochure weight is 10600# and estimated weight with normal loading is well over 11K, maybe closer to 12K.

So, the math is accurate, but it may not quite tell you the whole story.
Having said all that, you will quickly see that some well-known 30' to 32' double enders with fairly vertical and full ends have a "lot" of WL, and still struggle to exceed 6 kts. They are heavy with a lot of hull area below the water and it just takes a lot of HP to move them along.
As NA B Perry once said about the whole desirability argument concerning different boats, a long time ago, "they're all good boats" ---- for the right conditions and the right owner.

Photo attached. Us at about 7.1 kts on a windless day. Note the following wave - definitely 'hull speed'.
Fair winds and no head seas,
Loren

 

[seadaddler]

Tip

Back in 2001 I had a 2001 Hunter 290 and it was a demo boat
that the dealer used for sailing lesson's and demo sails so after
a year or two it was hard starting and so found out the fairly
new Yaynmar with low hours had a clogged mixing elbo and after only
cleaning it out and getting all the build up out from maybe too much idling
I put it back together looking very clean and cleaning the hull and the 2 blade prop it was like a new boat and I was sailing and motoring easy at 5 to 6 knts
with out any problems and if I really pushed would hit 6.5 if conditions were right,but most sailing was easy to do between 5& 6 knts.
Nick

 

[BarryL]

Hey,

I used to have a Newport 28 with the same engine. When the bottom was clean I could motor cruise at 6 kts. As the bottom (and prop) got worse the speed would drop. Does your tachometer work? Those engines like to run at 80-90% of max rpm. I would run it up to max RPM, then back off a few hundred RPM and see what that speed is. Don't be afraid to run the engine hard. I think more diesel engines are damaged by 'babying' then by running them hard.

Barry

 

[McIntoshUSA]

Hey,

I used to have a Newport 28 with the same engine. When the bottom was clean I could motor cruise at 6 kts. As the bottom (and prop) got worse the speed would drop. Does your tachometer work? Those engines like to run at 80-90% of max rpm. I would run it up to max RPM, then back off a few hundred RPM and see what that speed is. Don't be afraid to run the engine hard. I think more diesel engines are damaged by 'babying' then by running them hard.

Barry

The book on my engine says that the max RPM is 3200. I have read that I should cruise at 75% of max RPM whitch is 2400RPM. The highest I have pushed it to is 2600 RPM. I didn't know if I would hurt the engine if I pushed it up much more than 75-80% of mas RPM. Yes our Tach does work.