E32 Repower, New Prop

I have recently re-powered my 1978 E32 from the old Yanmar 2QM20 (20 HP at 2600 rpm and 2.14 gearbox) to a Yanmar 3YM20 (21 HP at 3600 rpm with a 2.21 gearbox). The new engine fits nicely in the compartment but required extensive modification of the rails and a 3” shaft extension.

My old prop is marked 14X14 but has small cracks and, according to the prop shop, is bent. Performance with the old prop is as follows:
· Max rpm is 3200 (6.7 to 7 knots with fresh bottom paint..with and against the current)
· 5.5 to 5.9 knots at 2000 rpm
· 5.9 to 6.1 knots at 2200 rpm
· 6 to 6.5 knots at 2400 rpm
· 6.1 to 6.8 knots at 2600 rpm.
· The 14 inch prop clears the hull by about 1.25 inches.
· Significant vibration above 2200 rpm.
· Pull to port, increases significantly above 2200 rpm.
· I have a one inch shaft.

Speed readings were via gps. RPM were from new Yanmar tach.

I am not a racer, and after shelling out for the new engine and installation, have a rather thin billfold. No luck finding a used prop at Minnie’s or ebay. My own calculations suggest a 14X12.5 or 14X13 in a two blade. A three blade is also a possibility.

I would appreciate any help you can provide re:
· Which prop (2 or 3 blade, manufacturer, pitch, diameter)?
· Where to buy?
· How does the Martec fixed two blade compare with the Michigan wheel sail two blade?

Kirby
Uff Da, E32, Alamitos Bay, California

I'd take a look at a flex o fold. I've heard a lot of good things about them and nothing negative. I think you could get into one of those for about $800. Once I have visibility on what my repower is going to run, I will likely add that to the visa bill. For my 38, I believe the price is just shy of 1000.

shaun

There are some conflicting goals in this situation...

The most "thrust" against an adverse wind and wave in a tight channel will call for lots of blade area. More blades, like 3 (or even 4!)= more area.
The most drag under sail will be a direct by-product of "more blade area."
:nerd:
You probably already know that a feathering prop will give you many of the benefits you would really like, but only at a price. The current price for my bronze Martec two-blade Featherer must be close to the $1100 or $1200. neighborhood. The last time I priced a fixed two blade for my boat it was around $300. (FWIW, I paid about $975. for my featherer a decade ago.)

To reduce drag under sail and stay with a less-expensive fixed prop, go with narrower blades or fewer (i.e. two) blades.
Then there is the issue of the shape of the blades... My featherer has no cupping to the blade design. This is what makes it straighten out the pitch on both blades, i.e. "feather" when sailing. This also reduces efficiency a bit.

It gets more complicated. The most prop walk in reverse will usually happen with the biggest fixed prop. The featherer (mostly) cures the prop walk Blues. I really love that feature.

For a selection of used props, at prices ranging from refreshingly low to enthusiatically overpriced, start calling the used boating parts stores. We have one in Portland, and there are one or two in Seattle. They always have a bench covered with props. Also, check with marine shops that sell and recondition props -- they may well have or know of one taken off another boat. Call Martec direct (or stop by, since they're in the Long Beach area)... asking about your options costs you nothing.


Best,
Loren in PDX

Loren, you didn't talk about folding props...

Loren, your post was very helpful in listing advantages/disadvantages, and mention of fixed and feathering props, but didnt mention folding props. My understanding is that the newer folding props (varifold, etc.) provide equal performance to fixed props, without the drag. Any thoughts?
Frank.

To Fold or not to Fold...

If you want the least drag under sail, and if that's your number one goal, then yes you do want a folder. Just how many nano-knots better than a featherer, I do not know for sure.

I am familiar with the non-geared folders and it seems like, sooner or later, they will leave one blade folded when you are depending on it for a bunch of reverse thrust when docking...
The "pure" folders do have one advantage: fewest moving parts to wear and break, and therefore less drag from the smaller hub. More nano-knots, but still... when you want the most efficiency under sail, you look at things like that.
:nerd:
Also, for many sailors and most cruisers, simplicity is always the holy grail of virtues. The fixed prop is therefore number one on that list, with the proven Martec (and any similar competitors') folders second. After that, you gotta choose the level of technology that still lets you sleep well.

I decided to ramp up to a featherer to get the reverse power and less prop walk, with speed under sail a wonderful bonus. I have a friend that loves his AutoProp. Like anything that lives in the sea, the later could, theoretically, have a bearing problem with small critters in the gears... and thereby have a balance problem. And so could any geared folder...
Heck, if I failed to keep good grease in my featherer, it could allow stuff to take root inside the hub, too.

Another way to say it is that there are no "right" or "wrong" answers. We all have the pick the level of technology and engineering that we are comfortable with, and what compromises we can adjust to easiest.

Opinions rendered daily, deposit .02 please.



Loren

Thanks, Loren. Your opinions are much appreciated!!
Frank.