Repowering? Bigger is better?

[Jim Cate]

Since Beta is utilizing Kubota engines (IIRC), and really only marinizing them inhouse, I have to believe that Kubota is the one who decides how to set up the engine as far as camshaft profile, injector characteristics and so on. The Kubota folks supply engines for a wide variety of applications -- tractors, forklifts, whatever -- and thus may do some fine tuning for specific needs. I suspect that is why these nearly identical engines exist in the marine world.

And for Delancy, as you consider the feathering prop, do remember that while they are versatile, they are inherently less efficient than other props due to there being no twist in the blades. You seem to be concerned about motoring range, and there is a significant loss between the feathering prop and either a fixed or folding model, both of which can use twisted blades.

Cheers,

Jim

[Delancey]

Originally Posted by cwyckham

Displacement and Weight are the same thing.

I wonder if for a guy like Andrew one means a calculated displacement and the other means what HIS boat is actually going to weigh in the slings with all his stuff onboard? I could be wrong.

[cwyckham]

Originally Posted by Jim Cate

Since Beta is utilizing Kubota engines (IIRC), and really only marinizing them inhouse, I have to believe that Kubota is the one who decides how to set up the engine as far as camshaft profile, injector characteristics and so on. The Kubota folks supply engines for a wide variety of applications -- tractors, forklifts, whatever -- and thus may do some fine tuning for specific needs. I suspect that is why these nearly identical engines exist in the marine world.

And for Delancy, as you consider the feathering prop, do remember that while they are versatile, they are inherently less efficient than other props due to there being no twist in the blades. You seem to be concerned about motoring range, and there is a significant loss between the feathering prop and either a fixed or folding model, both of which can use twisted blades.

Cheers,

Jim

Great point, Jim.

Thread drift: What other pros and cons of folding vs feathering are there in your mind?

[Delancey]

Originally Posted by Jim Cate

Since Beta is utilizing Kubota engines (IIRC), and really only marinizing them inhouse, I have to believe that Kubota is the one who decides how to set up the engine as far as camshaft profile, injector characteristics and so on. The Kubota folks supply engines for a wide variety of applications -- tractors, forklifts, whatever -- and thus may do some fine tuning for specific needs. I suspect that is why these nearly identical engines exist in the marine world.

And for Delancy, as you consider the feathering prop, do remember that while they are versatile, they are inherently less efficient than other props due to there being no twist in the blades. You seem to be concerned about motoring range, and there is a significant loss between the feathering prop and either a fixed or folding model, both of which can use twisted blades.

Cheers,

Jim

I will certainly be doing some forum searches on the subject but its good to note up front, thank you. As with most things it seems, always a compromise. I am not necessarily obsessed with range but if it comes my way I'll take it. I like to try to keep an eye on the big picture if I can and have all my bases covered, hence the mention at this point is for academic purposes.

[Delancey]

Originally Posted by Jim Cate

they are inherently less efficient than other props due to there being no twist in the blades.

In other words, they end up delivering less thrust per horsepower? Light air performance is a concern for me but if I am trying to go with an undersized engine maybe those two don't work together so well.

How do folding props compare in efficiency compared to the feathering variety? Again maybe not so good for the undersized-engine approach when considering trying to go in reverse which I understand is not a strong point for folding props as they can potentially collapse in reverse ?

[Jim Cate]

Originally Posted by cwyckham

Great point, Jim.

Thread drift: What other pros and cons of folding vs feathering are there in your mind?

Well, here goes:

Folding Pros: Minimum drag sailing, lower cost than feathering, good efficiency going forward, long service life, simple mechanism so very reliable.

Folding cons: non-adjustable pitch, less thrust in reverse except at max RPM, more expensive than fixed.

Feathering pros: good static thrust in both forward and reverse, many models have easily adjustable pitch, lower drag than fixed while sailing

Feathering cons: Expensive, poor efficiency, complicated mechanisms, some models are reluctant to feather whilst sailing, higher drag than folding, but better than fixed, in smaller diameters the size of the hub (containing the gears to rotate the blades) means that the actual blade length is shortened and thus blade area reduced (I'm not sure how big a deal this is, but one NA that I spoke to was concerned).

The main complaint about folders has traditionally been poor performance in reverse. Some designs (notably Flex-O-Fold) have tested surprisingly well in reverse. I suspect that the folk wisdom is based on the need for high RPMs in reverse to get the blades fully extended and thus to get good thrust generation. I know that I have a hard time doing this on our boat, for the noise and apparent thrashing is sorta embarrassing, and I cringe when it is required! In the testing situation, the max thrust is indeed measured at max rpm, and the testers don't have to put up with scathing stares from their dock neighbors. Note that this is conjecture on my part - no documentation is offered!

Anyhow, that's my take on things. I have had two and three blade fixed props, two and three blade folders of several makes, and three blade feathering. My definite favorite so far is our three blade F-O-F folder. YMMV.

Cheers,

Jim

[Jim Cate]

Originally Posted by Delancey

In other words, they end up delivering less thrust per horsepower? Light air performance is a concern for me but if I am trying to go with an undersized engine maybe those two don't work together so well.

How do folding props compare in efficiency compared to the feathering variety? Again maybe not so good for the undersized-engine approach when considering trying to go in reverse which I understand is not a strong point for folding props as they can potentially collapse in reverse ?

Yes, exactly: less thrust per hp on the shaft.

Either feathering or folding will give reduced drag over a fixed prop, with folding being somewhat better. The benefits from this are considerable, and are most notable in the mid range of speeds. In very light airs, skin friction on hull and appendages is the biggest factor, in strong winds as you approach hull speed, wave-making is the culprit. In the middle, propeller drag is a big factor, and this is where the fixed prop kills you... and these conditions are where you spend the most of your sailing time IME.

Good folding props have efficiencies similar to good fixed props, and should not be a detriment to your proposed low power setup. See my earlier post for my thoughts on reverse thrust with folders.

Cheers,

Jim

[Delancey]

Awesome, thanks for the breakdown! The OEM prop on my boat is 18" but I think I might have room for more, other than cost or clearance are there other factors that limit prop size?

[Terra Nova]

Originally Posted by Stu Jackson

...larger bank...a lower daily draw down will make the bank last longer.
...the biggest reason banks fail is poor/chronic undercharging...

The larger bank is much more likely to remain undercharged.

Originally Posted by Andrew Troup

...I may retain the electric starting capability on the diesels...
I plan to build a prop with separate blades which plug into the boss via tapered splines...
I don't plan on using electricity for bilge pumps. I won't run electrical wiring anywhere near the bilges, except for speed and depth where it's unavoidable...
For autopilot, I plan to have a couple of small-boat tillerpilots, one installed in a watertight compartment, operating the servo oar of the windvane steering...

Electric starting is easy--most engines already come with it. But a way of hand-starting could be of great value.

The prop seems an unnecessarily complex project for something that can be so simple, and is so easily damaged.

Manually operated and engine-driven bilge pumps are SOP for bluewater cruisers. But every boat should have an automatic electric pump, for while the boat is unattended. This same pump could serve as a shower sump. It is quite a simple matter to make its electricals waterproof.

I also plan a Tillerpilot to run my wind vane. But I love your idea of having it enclosed!

[Delancey]

Hand start the 10 and use it to start the 20?

[JPA Cate]

Delancey:

Relative to our experience with folding vs. feathering prop, something Jim didn't say, when he mentioned loss of efficiency with the feathering prop was that in our case, it was experienced as a 25% increase in fuel consumption, which came as a surprise to us that it was that much!

Ann

[Andrew Troup]

Originally Posted by Delancey

I wonder if for a guy like Andrew one means a calculated displacement and the other means what HIS boat is actually going to weigh in the slings with all his stuff onboard? I could be wrong.

Well it was target displacement, which relies on me achieving my target weight, (because as everyone seems to realise, displacement is the same as weight .... unless the keel is touching, or the docklines were too tight when the tide went out!)

but that target is at half-load (eg, inshore sailing).

In my case I will have a reserve to supplement the nominal 30hp for short bursts (say for setting an anchor, or forcing the bow back up into the wind if I 'lose it' momentarily )

because the accumulator will be able to supplement the hydraulic oil supplied from the prime movers, up to whatever I judge the bottom end of the drive unit (cannibalised from a saildrive) can take.

[Andrew Troup]

Delancey

I forgot to answer your question about alternators: I plan to leave the standard units on the engines. And (probably) the starter motors, as I mentioned. I don't think hydraulic starting using a hydraulic pump as a motor is a sensible mainstay.

I don't mind electricity, I just don't trust it (around salt water) for doing essential heavy-lifting-type work.

And certainly hand-starting the wee donkey in order to jumpstart the biggun is on the playlist if needs must. I'm sure (if the 1GM were defunct) even the 2GM could be started at a pinch with a capstan fitted to the crankshaft*, and either wind or water power.

... or possibly even by human power, if the oil and coolant were taken out and heated to running temp - otherwise I think there would probably need to be a layshaft at waist-height, with a coffee-grinder-type pair of handles, and a foot control to trip the decompressors, which is way too much trouble).

*I just went out with a tapemeasure; the crankshaft pulleys have different ODs but the spigot bore and (puller) bolt pitch circle I plan to use for the capstan are the same, so the same drum could be swapped between engines without me needing to do any mods.

[Stu Jackson]

Originally Posted by Delancey

I myself am a big fan of John S. Letcher and maybe share some of your outlooks but am obviously dealing with a different stack of cards.

Yes, yes, yes. A great read. I've kept his book as a Bible for many, many years, glad I bought it.

But you're dealing with two different things:

1. The boat will work as a sailboat with Letcher's ideas. Superb.

2. You will have an engine. WHATEVER engine you select WILL have an alternator. Right? So, the ONLY issue you're realing with is how the boat will be propelled with that particular engine, 30, 35 or 38. They ALL WILL have an alternator (please, pretty please, stop calling it a generator, it's just confusing...). That alternator WILL produce amperage WHEN the alternator, i.e., engine, is running, right? So, what's the deal, no need to get hung up on that PART of the total package, since if you do it right, you'll have an adequate amount of solar.

ALL of the engines you are considering will HAVE ADEQUATE hp to drive an alternator, and if you use the previously mentioned SEM or amp manager features of an external regulator, WILL work.


Narrow it down to that and it should make your selection issues much easier.

Good luck.

[Stu Jackson]

Originally Posted by Terra Nova

The larger bank is much more likely to remain undercharged.

Huh? That makes little sense with a properly designed system.

One must look at it simply this way:

Regardless of the storage capacity, what goes out must be less than what can be returned on a daily or periodic basis. Thus, any SIZED PROPERLY sized house BANK will do just fine.

Can you hep me understand this seeming anomaly?