Hunter 40.5 two blade prop broke in half! Need new one.

[Rick D]

Maybe...

Did you notice better fuel economy and higher speed VS rpm at cruising speeds 5-6k?

Gori offers a 18x13 I think that should be good eh?

http://www.defender.com/product.jsp?path=-1|311|53222|297678&id=146208

You should first check directly with any of the propeller manufacturers before ordering since the hub may make a difference. Just give them the stock two blade spec's and they can figure it out from there.

I did not notice any difference in fuel consumption.

 

[Dennisail]

What about revs? Did they come down a bit with the over propping or also no difference?

I just found my survey listed the prop. It says its 18x15 rh. 1-1/4", so that corresponds to your findings rick.

 

[Rick D]

REV's vs. Speed

What about revs? Did they come down a bit with the over propping or also no difference?

I just found my survey listed the prop. It says its 18x15 rh. 1-1/4", so that corresponds to your findings rick.

I dropped about 300 RPM for the same speed. Nice, quieter, not so busy but not so good on the engine and the too steep pitch reduces the ultimate thrust.

 

[Dennisail]

Yeah that's beneficial at sub max power IMO. I think you will find if you look at the power chart of your engine and the power delivery chart of any prop you will find that the engine curve bulges up and the prop curve goes the other way. What that means is that when a prop which is geared to deliver max power of the engine, there will be a massive excess of available engine power in the lower RPMs. In other words it will not be overloading the engine at lower revs with too big of a prop and you will be getting more power into the water at lower revs. This comes at the expense of overloading it at high revs, and max power loss as the engine never reaches max power.

For me that is fine as I never run anywhere near max power.

radom pic I found

You can see the prop is chosen here so the prop curve aligns with the engine power at just over 4000rpm (which will allow max speed as that is close to max engine power) but at 2000rpm the engine can produce around 3 times more power than the prop can transfer to the water!

If they really only cared about top speed they could reduce the pitch even more so the curves lined up at 4750rpm. This would result in horrible low RPM performance though!

 

[Rick D]

Yea, except you don't want to load up the engine with carbon. High speed diesels HATE that, so I have read, and so my prior Yanmar's mixing elbow confirmed...

 

[Dennisail]

I ran my yanmar at 1700rpm for economy (small tanks and limited fuel in the pacific 0.5G/H @ 5K), every now and then I would run max power to blast the carbon out. I guess if you cant rev it as high to blast it the carbon out, that might be a draw back. However running a diesel at low load is also bad. So overproping it will load it more at lower revs (where it is normally grossly underloaded) so you win some loose some there.

 

[Marco Garcia]

Hi Dennis,

Just in case you need them.. i found this picture of the gear box and a table for fuel use... maybe it is not correct, but at least is a safe bet for usage...

2.63 ratio

 

[Dave Groshong]

Hunter says they used 2 props, depending on whether you have a Yanmar or Volvo engine. I promptly left the information on my desk, but will get back with you tomorrow.

 

[Dennisail]

Thanks guys! That fuel table could be handy!

I went swimming today. Lovely water in my marina.

Prop (what was left of it) and shaft covered barnacles. Zincs were still there but may have been nothing more than oxidization. So I replaced them. Cleaned everything up etc. Maybe the barnacle growth helped to break the prop? Over a year ago my surveyor said I should have it removed and checked as it seemed it was not 100% true. Possibly it took a hit before I got the boat?

Prop embossing: Martec RH18DX15PX111/4

So that appears to be exactly the same as Ricks prop.

Trans ratio stamped on back of box. 2.63

 

[anchorclanker]

I would pull the boat and inspect everything. There could be a lot of reasons to lose a blade other than corrosion. It could have had a vibration that you wernt even aware of, or could have been whacked at some point in the past causing a crack that finally let go.

Also, with all the different engines, gearbox ratios and shaft sizes, whats on one boat, even the same identical boat, has little bearing of yours. You also cant go by rated horsepower. Two different engines of equal power (Volvo vs Yanmar, for example) will produce their power at different rpms, and even if all else were the same, require a different prop.

If the prop you had worked well, that should be your starting point. Even if the numbers are gone and a blades missing, a prop shop can determine its original pitch and diameter.

 

[Dave Groshong]

Yes, that's the spec Hunter just gave me for that boat with a Yanmar engine. Give me a call if you'd like a quote.

 

[Dennisail]

Note the specs I gave recently are directly from my boat. I didn't go swimming in the marina for leisure! However this does match up to exactly what others have found.

Yanmar 50 hp 4JH2E Box ratio 2.63. Stock prop 2B 18D 15P 1-1/4 RH

Dave PM sent.

 

[Dennisail]

OK guys.

I just purchased a used Flexofold prop which came out on top in the prop test of 15 props. I got an amazing deal (provided its as good condition as they say and fits!)

Would anyone like to guess how this will perform compared to my old prop as its not the same pitch and diameter?

Flexofold 2B prop: 17" - 17P (possibly 17.5P as they had to measure it)
Standard 2B prop 18" - 15"

I think that the extra pitch will make up for the diameter loss (with some efficiency loss at high speeds). Possibly this will also me more efficient when motor sailing? Either way the price was too good to refuse. $450.

Thoughts?

 

[Steve Dion]

I would suggest that you contact the mfg and ask the what the specs should be before you waste time & money on having a prop installed and then having to remove it and having it reworked.

 

[Dennisail]

I will ask. However I am pretty confident that this arrangement will be OK.

 

[heart of gold]

Check your props color. If it is pinkish, that means electrolysis has sucked the zinc out of the bronze. Once this happens the metal becomes very brittle, of so says the mechanical surveyor who looked at my boat originally. Are your shaft zincs in good shape? Cheers

 

[kloudie1]

Besides the prop, the strut should be carefully checked for electrolysis.. Usually if a prop slings a blade, the strut is not far from breaking itself. When my prop slung a blade, the strut broke immediately because of the vibration.. then the shaft bent .. The prop and shaft had both been electrolytically corroded.

 

[Dennisail]

The strut still had very good zinc left on it (but I replaced it anyway). From what I could tell underwater the strut was in good condition. As soon as the prop broke I reduced RPM and did not run it for more than a few minutes at a max of 1300rpm, just to get into the slip.

The shaft still had a zinc but I think it was totally oxidized. So I put a new zinc on it. The prop was not pinkish.

The prop was and always has been loose on the shaft. As it I could move it by hand a small amount. Is this bad?

I hope my prop shaft is not bent or corroded. What is the standard way to check for shaft runout. A dial gauge?

 

[eianm]

I moved from the factory standard 2 blade to a 3 bladed variprop- what a wonderful difference that made( greatly reduced vibration, quicker take up and more power/ faster. However, if i were to do it again, i would definietly go with the GORI- it has the overdrive function which is amazing- in overdrive you can drop around 500+ revs for the same hull speed- a big fuel saving over a distance.

 

[VINN]

same thing happened to me several years ago in my new slip in point lookout. the blade just fell off as I was leaving the slip after a 4 month stay for the winter. a kind gentleman next store told me to hang a zinc guppy over the side because there was allot of stray current in the water, and I told him I just put a new zinc on the shaft. he grinned and said maybe it will be ok. I dove under in march for severe vibration and 1/2 of the prop was gone and so was the zinc. the lesson... new prop cost 550. the guppy was 50$ and is still going after 5 yrs. and it was no picnic changing the prop myself in 41 Degree water. i presume the zinc on the shaft lasted only 2 months. the good thing about the guppy is you can inspect it anytime without going under the boat, if you suspect high rates of electrolysis. for some reason it lasts allot longer than the zinc on the shaft?