Overpropped/Overloaded, fix it or just live with it?

[stormchaser]

It seems I'm a bit over-propped. I can only get up to about 2,100-2,150 n gear even with a perfect bottom. This seems to conincide with moving onboard and adding a LOT of weight. She used to plane off very cleanly and topped out at 17.9. Now she won't plane off cleanly and tops out at about 15.5. So, my guess is that the extra weight has caused an overload problem. Otherwise the engines run perfect, staying right at 185* even after 20 in at WOT. WOT in neutral is right where it should be.

The port engine has been majored (about 650hrs since MOH) and does not smoke and starts instantly even without the blockheaters. Starboard engine needs to crank 15 second and smokes quite a bit if started without the bockheaters. With the block heater on, starts instantly with almsot no smoke, so I know she's a bit tired.

I now I should start planning for a MOH on the starboard in the next few years, but she barely gets 100hrs a year so I'm hoping to keep her going as is for a while.

So...what's the consensus? Shgould I get the props reworked to knock some pitch off? What effect will that have on speed and efficiency? I typically rcuise at 9-10 knots but do like to periodically get her out and run her a bit...sure would LIKE to get her back to being able to plane cleanly...but efficiency at 9-10 knots is also important.

So...thoughts?

 

[Genesis]

My opinion: Fix it if you intend to run on plane.

 

[stormchaser]

You think she might plane off cleanly with a little less pitch?

 

[SKYCHENEY]

You think she might plane off cleanly with a little less pitch?

No, but they won't be overloaded and you'll be able to run at a reasonable cruise rpm without worry of causing any undue stress to the engines.

 

[Brian Degulis]

It's going to do better on plane if you de pitch but who knows if it will plane cleanly. If you de pitch your going to do worse at 9-10 kts. You'll have to increase RPM a little and you'll be loading less. At 9-10 kts your already loaded very light. So you have to balance the ability to plane well against a little better fuel mileage and a little better loading at slower speeds. Don't run them @ wot if your not getting the full RPM that will kill them pretty quick.

Brian

 

[REBrueckner]

I'm with Brian on post #5.

That "old" engine will likely outlive you!...a little smoke means very little. At 100 hours annually that engine is likely to still be smoking a bit in ten or 15 years, just like now. If you wanted to run hard and fast, maybe it would make some sense to plan for a rebuild in a few years, but even then if the two engines make about the same top RPM why bother?

I would check stbd engine exhaust manifold temperatures at around say 1500 to 1800 RPM with an infrared thermometer to make sure all eight cylinder exhausts (before the water cooled portion of the manifold) are about the same temperature....that's a cheap, fast and easy test to make to be sure you are getting reasonable combustion in each cylinder...and you can compare the temperature variations with your "strong" port engine.

I don't recall my variations so maybe somebody can offer a target range....I'd guess temps with 6 to 8 degrees vairation should be fine....

My 1972 8v71TI's on a 48YF were just like yours...overpropped by about 150 RPM, port 'rebuilt' by me, due to scored cylinder liners, stbd smoked a bit more...for 11 years, currently about 2,700 hours. When I had oil analyzed at my purchase, stbd eng chrome (rings) was high (although it was not flagged by the lab and I did not realize it).

After about 1100 hours use by me, 10 or 11 years later, last year I think, the chrome reading was quite a bit LOWER but this time WAS flagged by another lab....turns out the first reading was very high, still don't know why, but that "old" engine passed survey earlier this year and runs fine at WOT.....about same RPM on both engines.

 

[stormchaser]

OK, sounds like I will be pulling the props and sending them to Black Dog...thanks for advice everyone...

 

[SKYCHENEY]

OK, sounds like I will be pulling the props and sending them to Black Dog...thanks for advice everyone...

What props are on there now? Are they the originally specified 28x32's? FWIW, I took pitch out twice to get loading right at cruise. Mine are now 28x28.5.

 

[stormchaser]

Honestly I don't know. The props came on her when I got her and I never really looked. Its probably in the survey. I plan on giving Black Dog Props a call and let them do the work. With PropScan, the props can be tuned to a GREATER level of acuracy than ISO Class 484/S (high accuracy). A typical off the shelp prop is ISO Class 484/III (wide tollerance)They did a GREAT job on the prop on my trawler. I got an extra .5knots at the same RPM or a 10% decrease in fuel use at the same speed (if that doesn't sound like a lot, remember this boat cruised at 7.5 and topped out at 8.5).

 

[captddis]

Black Dog is great, I used to ship props up to them for tuning. Larry told me there was a prop scan shop in Cape Coral so I use them now. The previous owner of my boat banged the props up in 1988. He had them reconditioned many times but the speed was off by 1.5 to 2kt from what it was even though the boat ran pretty smooth. Fast forward to 2004 I sent the props to Cape Coral for tuning and Randy the owner called me and asked what happened, I told him the story and he said that he could tell that the blades were folded and straightened but never twisted back correctly. He sounded so negative that I asked if I should buy new props, He said " no I am confident we can make them right"
The speed came back after 16 years and the props are silky smooth.


A lot of shops have the Prop Scan or other computer scan equipment, but you need someone who understands the info the computer spits out and can hammer the prop back into shape as per the scans. Many can't.

 

[krush]

I use this guy: http://www.murphyspropellers.com/

 

[stormchaser]

What level of accuracy do they tune to? Upon further research, it looks like Black Dog onoly tunes props to level II not S. You can buy new S-tuned props but with refurbishing it only gets them to level III and I really want better than that if I'm going to go through the time and expense of having the work done.

 

[REBrueckner]

ok, so let me see if I understand: you have a 25 year old boat, 25 year old engines, you run only 100 hours annually, you experience no noticeable vibration, you cruise around 10 knots presumably to economize on fuel consumption, and you are still hung up about the final nth degree of tuning on your props...(why, you sound a lot like me!!)

things must be good with you Dave, real good....

anyway, for another touch of input: go figure your approximate payback on whatever it is you decide to do on your props: as an example, figure expensive fuel with Obama in charge for 3 more years, say $5 a gallon, and 15 gal/hr use; at 100 hours/yr roughly $7,500 annually. (5 x 15 x 100).

So you get your props tuned for, what a thousand dollars? (plus, maybe, removal, and reinstallation costs?) ....say you gain 2% efficiency...2% of $7500 is about $150 savings annually .....1000/150 a payback of maybe 6.7 years or so....(with the numbers I've assumed)....no so good, but not crazy,either

if 3% improvement, about 4.4 years payback...


For the admiral: better assume a whopping 3% efficiency increase; This may be the type logic necessary to help "convince" your admiral of the wisdom of THIS venture.....good luck. But likely a dinner out will work better.

 

[Brian Degulis]

What level of accuracy do they tune to? Upon further research, it looks like Black Dog onoly tunes props to level II not S. You can buy new S-tuned props but with refurbishing it only gets them to level III and I really want better than that if I'm going to go through the time and expense of having the work done.

For years and years all that was available was prop recon. Which is basically putting the prop up on blocks that match the pitch and beating them into shape. Smooth out and dings balance and your done and it works.

Now we have prop scan much better than the old way. The lowest level of propscan will make your props better than new, much better. You would likely see no diffrence at from level 1 to level 3 other than the expense. For a high perfomane boat running 25Kts the higher level may be worth it. In your case it's not.

If your still determined to go to the highest level then General Propler in Bradenton FL can do it. We use them they do a lot of OEM work good quality and fair prices. Your props can ship UPS.

Brian

 

[DLCameron2]

Hello Storm-meister:

Try S & S Propellers they are in NY. http://www.sspropeller.com/services/

What everyone is saying is true, lots of $$$$'s for a lil improvement. Now if you want to re-gear it etc., then that is a horse of a different color; cubic dollars and major difference in performance.

My 2 cents.

DC

 

[krush]

Why not wait until you hit something and bend a blade before spending time and money to get the props worked.

 

[TopHattandTails]

Fwiw- class III is plenty on a 53my. Whatever route you go, make sure you get paperwork. If you hit something, you can tell the insurance company that you require your props back to whatever spec you had via the paperwork as proof.