Prop size question

[GILow]

Originally Posted by a64pilot

Then you want one of the feathering props that are flat plates as they work the same in reverse as in forward.

Or an Autoprop, because an Autoprop blades actually reverse direction so the leading edge is still the leading edge in reverse.
It’s hard to find, but if you look you’ll find that the Autoprop was designed way back in WWII, specifically to get a landing craft off of the beach, they were after max reverse power.
We want good reverse power, but if your stuck on the beach and being shot at, you need good reverse power.

Cool fact about the Autoprop, I'll share that one with my son who loves that kind of WWII historical stuff.

I've just bought a Kiwiprop, it was the only feathering prop in my budget and it is due to arrive this week.

I have spoken to a few Kiwiprop owners. They all assure me reverse will be great. (They also reassured me that if I follow the maintenance instructions I will have many years of trouble free use, as they have.)

[Compass790]

Originally Posted by MicHughV

....I have to echo Compass 790 thoughts here....
....if you think you are going to make 8 knots with only a 12 hp engine on your size boat, it is time to put the crack pipe down !!!

Sorry MichughV you had already pointed it out. I was echoing you! pays to read all previous posts. I know this but frequently rush into posting before reading whole thread
Still, guess repeating it may help hammer it in.

[MicHughV]

Vancefish, I'm going to do you a big favor and give you a reality check what your 12 hp engine is really capable of doing......no matter what prop you have on.

Take your boat out to sea and try to motor into a 4-6' headsea. Note, I say 4-6', which is relatively small wave height.

This is what is going to happen.

In between wave sets, ie, the trough, you will maybe do 1-2 knots....maybe.....each wave you try to climb will reduce your forward motion to around 0 knots, possibly even going backwards.....not only will it reduce your speed to 0 knots, without speed you won't have steerageway and you will spend valuably seconds getting the boat pointed in the right direction again after each wave has passed.

Once the wave has passed, your boat will have a scant few seconds to build up speed again before the next wave face...hence the 1-2 knot likely speed in the trough.

After doing this for an hour, you will find that you have probably covered a distance of about one nautical mile.....hopefully sufficient time to come to your senses.

In the meantime, your boat will have been jumping up and down like crazy for an hour and the sludge in your fuel tank will have been thoroughly mixed adding another possible problem....a clogged fuel filter...

Listen, besides a 40 year career in marine engineering, I speak from experience, as I've been down this road before in my younger years.

If you want to power into a sea, you will need serious horsepower for your boat, nothing less than 40 hp, preferable more.....with shaft and propellor to suit....not to mention additional tankage.

You will be far better off trying to sail into a headsea....try to remember that you are on a sailboat, not a powerboat, if that is your only other choice...but you will find that most globe girdling sailors have found that wanting to go from Point A to B, often requires going to Point C first.

Sailing is not a " straight" line sport....

Lastly, ocean sailing requires an understanding of seasonal winds, currents, etc...many good books are available that can guide you through when is the best time to take advantage of favorable winds to go somewhere.

I know that boats have crossed oceans without engines, but this requires a special type of sailor...you must ask yourself if you qualify as to being such a sailor.

[FPNC]

13 x 9 , 3 blade, RH. Or a 14 x 8, 3 blade RH. Like a fixed Michigan Sailor 3 or MP3.

As that engine is probably not making even 11 hp, don't expect more than 6.5 knots at the best and you will fight wind and tide. Your under powered and would be better at 20 HP or even 25 hp if you are really loading her up for cruising.

Good luck!

[Vancefish]

I have purchased a 13.5" / 14" (350mm), Two blade Max-prop adjustable from 10 to 30 degrees.

After reviewing Grayhawk's (a sister boat) setup, running a 15hp Yanmar, with a 16", 8 degree Martek (curved blades). Then learning that a flat blade reduced the amount of thrust as well as drive line strain. Thus allowing a higher pitch.

I purchased this used prop.

10 degrees is this props minimum pitch, which to me looks like NOTHING!.. honestly I can't imagine my Diesel engine couldn't spin this thing to my max RPMs..

It does need new grease, after a good cleaning.

What sort of Grease should I use for a fully submerged thing?

[Vancefish]

After talking to the seller extensively..

This Prop came off of his Catalina 30, With the exact same engine as my Peterson 34.. A Universal 5411. After his boat was damaged in a Florida storm.

My boat is 10,800lbs.
The Catalina weighed 10,200lbs

My Peterson has a slightly sleeker hull shape but is otherwise fairly comparable.

He had this Propeller set to 12 degrees, telling me he never saw any smoke underway, and could reach full RPMs without issue..

My boat has slightly less drag due to hull shape, but more weight (600lbs)..

So should I aim for 10deg or 12 deg? [emoji848][emoji3166]

[kenbo]

Originally Posted by Opie91

That prop is way too big for 12 hp per Campbell Sailor. They recommend a 12x6 for a 16hp and a 12x7 for a 20hp.

I started with a 12x7 on my Beta 20 and ended up with a 12x6 and it is still a little too big. It fells smooth as can be, but it feels more like there is a (smooth) blender down there than a propeller.

If you haven't figured it out I'm not a big fan.

I had planned on replacing it this year if you want a 12x6 1" taper shaft I'll sell it shipped for $200 to the continental US.



No Refunds.....

Opie's right about the sizing of the Campbell sailor, you can't use a standard prop calculator since the blades are cupped and ogival shaped. That 14" is too large for your 11 not 12 hp engine.

[kenbo]

Originally Posted by Vancefish

After talking to the seller extensively..

This Prop came off of his Catalina 30, With the exact same engine as my Peterson 34.. A Universal 5411. After his boat was damaged in a Florida storm.

My boat is 10,800lbs.
The Catalina weighed 10,200lbs

My Peterson has a slightly sleeker hull shape but is otherwise fairly comparable.

He had this Propeller set to 12 degrees, telling me he never saw any smoke underway, and could reach full RPMs without issue..

My boat has slightly less drag due to hull shape, but more weight (600lbs)..

So should I aim for 10deg or 12 deg? [emoji848][emoji3166]

On my prop calculator on your boat with a 12,000 lbs. displacement I get a 13" x 9" 2 blade. So your 2 blade MaxProp is 13.8" diameter so drop the pitch an 1.5" or so to 7.5" of pitch. From the MaxProp tables that's 16°. But of course that is always just a starting point.

[Vancefish]

This is the more accurately filled out Calculator on Vic-Prop.

As stated before. This Propeller was used on a 5411, in a similarly weighted Catalina, with no issues at 12 degrees.

Grayhawk (a sister boat) runs a 16" 8 deg on a 15hp Yanmar. They also reported being underpowered, but still capable.

As for "Power in rough seas"? I honestly have no intention of Motoring around in a storm. It's my opinion that a Sailboat's engine is for getting in and out of a marina. Nothing more!

Think Cruising Lealea.. They reduce sail, heave to, and rest until the storm passes. In the Doldrums they bob on the glass!

They do motor on occasion, usually to get into a port with no wind. As well as to charge batteries. However they only have one tiny solar panel system (two square feet of panels).

Does anyone know of a Calculator that deals with Flat bladed Props?

I've found numerous mentions of adding a few degrees of pitch to flat bladed props. Yet the only calculators I can find are for Curved blade and Motor boats.

[Vancefish]

This is 10deg of pitch by the way!

[Cheechako]

Originally Posted by Vancefish

I have purchased a 13.5" / 14" (350mm), Two blade Max-prop adjustable from 10 to 30 degrees.

After reviewing Grayhawk's (a sister boat) setup, running a 15hp Yanmar, with a 16", 8 degree Martek (curved blades). Then learning that a flat blade reduced the amount of thrust as well as drive line strain. Thus allowing a higher pitch.

I purchased this used prop.

10 degrees is this props minimum pitch, which to me looks like NOTHING!.. honestly I can't imagine my Diesel engine couldn't spin this thing to my max RPMs..

It does need new grease, after a good cleaning.

What sort of Grease should I use for a fully submerged thing?Attachment 207966Attachment 207967Attachment 207968Attachment 207969

That's a lot of prop and not much HP for your boat. I would normally go with the lesser pitch and see how it works. But yeah, there's not much pitch there at all. Go with 12 and see what happens. These can be adjusted in the water by a diver with knowledge. With that HP you are going to struggle in headseas anyway. Get every bit of RPM you can, or at least the max HP on that engines HP curve.

[Vancefish]

Originally Posted by Cheechako

That's a lot of prop and not much HP for your boat. I would normally go with the lesser pitch and see how it works. But yeah, there's not much pitch there at all. Go with 12 and see what happens. These can be adjusted in the water by a diver with knowledge. With that HP you are going to struggle in headseas anyway. Get every bit of RPM you can, or at least the max HP on that engines HP curve.

Thanks Cheechako!

It looks barely capable of pushing much of anything at 10 deg to me! [emoji23]

As I said, The previous owner's boat was CLOSE in LWL, Weight and had the same engine. He reported being very happy with this Propeller.. Until the boat was damaged.

He ran it at 12 degrees, and says he never blew black smoke, or overheated.. Which seems to be the Two things that being over Prop'ed are known to cause..

A sister boat GRAYHAWK runs a Yanmar 15hp.. With a 16 X 12 Martek folder.. [emoji2955] FAR more diameter, and 12 deg pitch!

My current Prop is a 14" X 7 Martek Folder. However the blades were damaged 18 years ago, before 15 on the hard. Honestly I doubt this is the engine from back then (Yanmar 15hp was OEM).. It is so out of Balance I hate to put it in gear!.. but I've never seen, even a puff of smoke..

It sure would be nice to find a Calculator that compensated for those flat blades!

http://sailing.thorpeallen.net/Greyhawk/Greyhawk.html

[Cheechako]

Originally Posted by Vancefish

Thanks Cheechako!

It looks barely capable of pushing much of anything at 10 deg to me! [emoji23]

As I said, The previous owner's boat was CLOSE in LWL, Weight and had the same engine. He reported being very happy with this Propeller.. Until the boat was damaged.

He ran it at 12 degrees, and says he never blew black smoke, or overheated.. Which seems to be the Two things that being over Prop'ed are known to cause..

A sister boat GRAYHAWK runs a Yanmar 15hp.. With a 16 X 12 Martek folder.. [emoji2955] FAR more diameter, and 12 deg pitch!

My current Prop is a 14" X 7 Martek Folder. However the blades were damaged 18 years ago, before 15 on the hard. Honestly I doubt this is the engine from back then (Yanmar 15hp was OEM).. It is so out of Balance I hate to put it in gear!.. but I've never seen, even a puff of smoke..

It sure would be nice to find a Calculator that compensated for those flat blades!

Peterson 34 Offshore Sloop GREYHAWK

That Max Prop will be far better than the Martec for sure. Martecs were low drag for the racing crowd but terrible props. Flat blades or not my Max Props have been every bit as good a 3 blade fixed... on 3 different boats.... and better in reverse than 3 blade fixed. Going to Max Props I never noticed any detriment in speed or fuel motoring in forward. I suspect blade shape makes more difference in higher speed boats than displacement hulls.
I think you have enough empirical knowledge from the sister boat to go with his setup. There's only so much you can predict and I have found prop shop predictors to be close but not right on for fixed blades even.

[kenbo]

Yeah prop calculators are estimates, they get you in the ball park. But I noticed a couple of things in your Vic Pro calculator that you may want to look check. 10,800 lbs is light displacement, you may want to add some weight for fuel, stores, water and passengers. The RPM of the 5411 is 3000 not 3600 and the standard gearbox on that engine was 2.0:1 I believe.

The calculator that I use, Propcalc, was developed at Cambridge University and has been very reliable over the past 30 odd years for me. It has worked well on MaxProps as well as standard props.

[Vancefish]

Well in my research I've discovered something..

When dealing with Standard Prop pitch. The second number (pitch) is determined by how far the "Screw" would travel through a substance in a Single rotation. Just like a Screw works!

Yet this Max-prop pitch is the Angle of pitch in degrees! 10 degrees off of flat.

Obviously my Propeller IS NOT going to travel 10 inches through anything at THIS 10 degree pitch.

So when I get back home, I'll devise a method of measuring the Travel distance at 10 degrees of pitch.

Maybe I'm still missing something.. [emoji2955][emoji848][emoji3166]