I found a lot of good info about props scattered about the site so I thought I would make a thread for all things prop.

I noticed this post from Mr. Christy:


Just wondering if Bengt made any recommendations as to what the proper prop would be? I think I am facing either a prop rebuild or replacement as mine is getting pretty floppy in the blades and they are tending to get stuck closed much more often.

If I am facing a replacement, I might look at a kiwi-prop. My slip-mate put one on his Santana 30/30 and he really likes it. He says the three blades make a huge difference to vibration levels. Does anyone have any experience on the J/30?

Picked up a new 2-blade Gori last fall. Hope it performs well, Ill see in the spring.

My old Martec was in sad shape when I got the boat, and I had it rebulit. 4 seasons later it needs anouther rebuild and I figured I would try a higher quality prop.

I've sent my prop back to Martec to have it rebuilt. Might have been something like $150? I don't remember exactly

One other note about the Martec's. I recently had mine rebuilt since it was quite loose. Apparently there are 3 different size bushings you can put in the prop when rebuilding - each time they have to go to the next size up.

When you get to the last size (which I have), that's it - no more rebuilds!

-djm

Rhapsody's prop was rebuilt by by sending back to Martec in 2009. The cost was ~ $230 and included drilling for over-sized pivot pin, weld buildup for blade stops, and machining back to original spec. It came back looking like a new prop.

So OK ... for background
1. photo of original pivot pin in drilled out hole




2. photo of pivot pin that depends on groves to hold in place


3. photo of cotter pins that hold the pivot pin in place
note that there is only so much room to redrill before the cotter pins will not work. see top photo

also refer to Additional data on Martec prop thread

I have the 3/4" shaft and it seems there are a LOT less options for replacements than having the 1" shaft. I don't think I can even get a Kiwiprop.

Scott,

Martec is quite reasonable. I bought a new Martec prop last year (to keep the integrity of the one design) and it really helped with vibration. As new props go, it's pretty cheap. Now I can reliably go backwards... bonus!

I am going to try a Gori this season. It seems to have a much higher build quality than the Martec. Plus I was out of rebuilds on the Martec.

Hope it quiets some of the vibrations!

Dominique,
By backward reliability, do you mean satisfactorily as well? I try to gauge if your new martec, in addition to reliability, makes the backward thrust significantly more efficient - even with our small 15hp YM?

It is still always stressfull for me to pull out of a slip with strong wind from the hip. I would love to have more thrust and less torque:-)

^ I always back into slips myself and I don't know why more people don't. You build momentum and steerage where there is more room and then getting out of the slip is a snap.

Georges,

I mean that I can actually get backwards. There was so much slop in my prop that I needed to get to at least mid range RPMs to get any thrust in reverse. Often the prop would not properly unfold either. I sent it to Martec for a rebuild but the metal was sufficiently pink that they could not guarantee the integrity of the prop if it was re-built. So I bought a new one. Immediately I noticed reduced vibration and real thrust at idle in reverse. Way easier to get out of my slip. Which I do entirely in reverse. Yes I am satisfied with the performance of the prop. Have not gotten into nearly as much trouble getting in and out of the slip since it was replaced.

I have been away but excited to weigh in on the Martec. I bought a brand new Martec 14x14x1 for Conundrum for 2011. I found the backing power and the braking to be lacking and wondered why. My Catalina 30 had the same prop and it was 15 years old and still had good backing ability as well as good braking power. Tha Cat has 4000# more to stop. I wonder why the J config is as it is. Is true for the rest of you, Poor backing and braking? I do go forward at 6.6 kt @ 2600rpm and Yanmar 13 2GM

Similar performance on Rhapsody to what Conundrum describes. I just learned to live with it. It is functional for reverse but not optimal. Then there is always prop walk when going astern. It's the nature of the beast and the design that is optimized for sailing upwind, not backing under power. I'll live with it!

My friend braved the frigid waters of Squamish today to pull my prop and see what we have to deal with. We had planned on turning some shims to take the play out of the blades.

These are pictures of the hub from either end, looking down the shaft bore hole. It definitely couldn't have been helping the vibration situation!

Absolutely send it back for refurb. As long as the hole for the pivot pin hasn't been over-bored too much with an over-sized pin used already.

Martec will weld up and refinsh the surface per my previous post in this thread.

Look closely. The problem is the bore hole for the shaft is nearly 1/4" off of centre. The hub will need to be replaced; it was ruined before it even left the factory 30 years ago.

We are actually going to try and machine a new hub if we can find acceptable stock bronze. Otherwise I will be ordering a new prop and hopefully it doesn't look like that.

ok - good solution. I couldn't tell that from looking at the picture. I thought you were referring to the pitting.

Before you do a custom fabrication ... call martec up ... it is a family run business and you may get the wife on the phone. I am betting they will give you either a new hub or one of their used, but good, hubs at no charge ... just tell them you have been living with vibrations and didn't realize their hub was the problem ... that has lead to a weak strut joint problem.

one of the props I sent in for refurb had slight fractures in the blades ... so the hub was good, but the blades were not. I got that back but unfortunately gave that old prop to someone who was going to polish it up for a wall ornament.

^Thanks Vic, I was going to let them know.

Upon further investigation the bore hole is actually centred with the blades and the yolk (good), but the cast itself appears to be off (i.e. extra material to one side). We think we can save it by turning the hub from the outside.

The blades have gone in to a local shop for some build-up and they will be refinished.

One question I do have:

Where is the hub or blades built up to stop the blades from touching at the tips when closed? we want to do it right.

look at the blades and you will see a closed resting point ... there is a similar resting spot for blades open there. I'm thinking there are matching surfaces in the slot inside the hub opening.

the metal apparently is soft enough to "dent" and actually wears off enough so that the blades no longer will be held slightly apart or "perfectly" aligned when open. this is on both surfaces. I'm thinking standard program of adding more metal than you need and grinding down prop stops to "perfect" space.

The surfaces "erode" away over time in salt water.

somewhere I have a photo of old blade vs new blade and the edges of the old blades are eroded to almost knife edges and the stop surfaces a mashed a bit. if I ever find it I have a "before" and "after" 15 years of use photo.

Down here they Paint the props and I am wondering it helps or hurts the metal.

Thanks! Big help!

Prop rebuild update:

Having old school engineers that like to monkey around as friends is a real blessing. Prop is now rebuilt and looking better than new for about $200 and a good bottle of scotch which includes in-water re and re.

Further investigation found that the blades were indeed off centre from the shaft. The hub has now been balanced, and the pin bored to 1/2" allowing it to be centred. The blades, probably due to pitting, were mismatched mass by 28 grams which has now been corrected and balanced together.

The test drive comes tomorrow after we put it back on, hopefully without dropping any parts!