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Old 10-17-2013, 03:56 PM   #1
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Hauled the boat out... installed a new prop

When I bought the Vashon, she had a 16x12 four blade Nibral prop, which I replaced with a 16x10 three blade. WOT RPM specs for my MD2030 Volvo is 3200-3600 and I was at 3150 RPM. Over the months, barnacles, running gear fouling, and added weight dropped my WOT RPM to around 3000 RPM. I installed a new three blade 16x8 high thrust prop and RPM at WOT is now around 3400 or so (within Volvo's specs). Mechanic noted that I have a large prop shaft (1.25" diameter) for my trawler's size.

Also added a manual "emergency" pump as a back-up to my two electric bilge pumps and the bottom was pressure washed.

I will be taking Sherpa on a cruise to Tarpon Springs next month so I wanted this addressed beforehand.
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Old 10-17-2013, 07:06 PM   #2
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In my opinion a Nibral prop for your type of boat is an overkill, bronze is more then sufficient and cost half the price.

If you supply me (by PM) the following data, i can calculate the prop for you.

Boat;
Lengths on the waterline:
Width on the waterline (if known):
Displacement:
Anticipated speed:________ in knots

Engine;
Make:
type:
No of engines:
Max output in hp/kW:________ at rpm:

Gearbox;
Make:
Type:
Reduction:________ :1
Rotation (LH/RH):

Propellor;
No of blades:
Max. diameter:________ (min. clearance of 0,15 x prop diameter)

Regards Cees
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Old 10-17-2013, 07:28 PM   #3
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Thank you, Reiziger but the new 16x8 prop is working just fine. Both the 16x10 and 16x8 are bronze--only the old 16x12 that came with my boat was Nibral.

Best,

Chris
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Old 10-17-2013, 07:57 PM   #4
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Nothing wrong with having a large shaft.
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Old 10-18-2013, 06:01 AM   #5
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What is cruise speed and RPM?
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Old 10-18-2013, 08:40 AM   #6
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Volvo specifically states that cruise RPM for my engine should be 300-500 below WOT... going "by the book" this means I should be at 2900 RPM cruise given the approximate 3400 WOT with my new prop. Having grown up around Lehman and Perkin diesels, I'm simply not used to these newer high RPM marine diesels.

Anyway, I'm taking the boat out this Saturday for some thorough sea trials around Tampa Bay to see how she handles with the new prop. I'm guessing my "cruise" speed should be around 6 knots at 2800-2900. I know what the math suggests, but I'm not 100% sure at this point.

With the old prop, I typically cruised at around 2650 RPM and achieved 5.6 to 6 knots depending on weather.

I will report Saturday evening or Sunday morning with my speed according to RPM. I'm happy the new prop puts me within Volvo's recommended WOT RPM specs--it should also address the troublesome prop walk I was experiencing.
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Old 10-18-2013, 10:22 AM   #7
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Quote:
Originally Posted by Vashon_Trawler View Post
Mechanic noted that I have a large prop shaft (1.25" diameter) for my trawler's size.
Come to think of it, I've never read a post where the boat owner was indicating that his shaft diameter was small in relation to the size of the boat.

Regarding Volvo cruise RPM, the Manatees like mine were mostly powered with 90, 100 and 110 HP Volvos. WOT is usually around 3500-3600. Most cruisers keep 'em at 2200 to 2600, or so I've read. The engines seem unaffected. Mine was replaced with a Yanmar 140 in 1991, and has very similar power and RPM characteristics with a 3600 WOT. I typically cruise at 2200-2600 with the same prop that came with the original Volvo 90. It feels right.
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Old 10-18-2013, 11:44 AM   #8
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VT,
Look how similar our boats are where it counts!


Willy's just a little bigger w 18" prop. The first pic is when we bought her .. in Edmonds WA. Bottom pic is at Craig AK w Nibral prop.

Sounds like your'e propped perfectly. My Yanmar in my Albin was a 3450 rpm engine and achieved 3400 at WOT. Cruised at 2750.

I'm surprised you paint your prop. Dosn't the copper in the paint damage the prop?

Yes your shaft is larger in dia than need be. Willy's is 1 1/4" too. That say's something about the designer/builder and there are probably other things over sized on the boat as well.

Lets see some more pics of Sherpa's hull.

I'm not impressed w the jackstand setup ... especially the rope. That should be a snug chain especially in view of the angle of the bottom and pad.

Third pic is our present prop ... Michigan MP bronze. Looks like you may have the same prop too. The one in the 2nd pic is an MP-3 nibral.
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Old 10-18-2013, 12:00 PM   #9
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You're right, Manyboats! Very similiar indeed! You have a very beautiful trawler. I am a sincere fan of the Willlard trawlers.

Not too many pacific NW style hulls in Florida waters and I get a lot stares and conversations. I'm amazed how well it handles in rough seas (I'll spare you my 4'-6' seas off of Egmont Key story)... my wife doesn't let me forget it.
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Old 10-18-2013, 12:48 PM   #10
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Eric,

Great shots of your boat! I'm guess your prop is 18x12?

I've included a few more photos of Sherpa's hull (clean and in the water after several months). Photos aren't the best since they were taken by the yard crew. Interesting about your comment concerning the painted bronze prop. Seems standard at most of the yards I've visited in FL. I wasn't aware there was a problem with galvanic corrosion with bronze props and copper bottom paint--I've never had a problem but will research the matter. I believe they also used a primer on the running gear as well--I can double check with the yard. We grow barnacles VERY quickly in Florida gulf waters and I'd be scraping the prop every week if I didn't protect it.

The prop is a Hung Shen Heavy Thrust. I've owned two and they've served me well. Yes, everything on this boat is overbuilt (not complaining of course) and everyone who works on Sherpa reminds me of it!
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Old 10-18-2013, 12:59 PM   #11
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Being in a cool climate I don't know much of anything about fowling props.
I just use a liberal application of ArmorAll in AK and hope that will work well enough down in WA. Big barnacles WILL grow on boats that sit for long periods of time though.

Yup the two hulls are so similar I can say I know almost exactly how your boat handles.
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Old 10-18-2013, 02:00 PM   #12
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With aluminum boats you are required to put an epoxy barrier coat on the hull before you use copper paint. I don't know if there is a conflict with copper and bronze or stainless but you should check the tables... Sorry, I don't have them handy.
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Old 10-18-2013, 05:22 PM   #13
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Quote:
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Being in a cool climate I don't know much of anything about fowling props.
I just use a liberal application of ArmorAll in AK and hope that will work well enough down in WA. Big barnacles WILL grow on boats that sit for long periods of time though.

Yup the two hulls are so similar I can say I know almost exactly how your boat handles.
Eric,

Just cruious, what is your prop's pitch?
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Old 10-18-2013, 10:16 PM   #14
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Vashon Trawler .............. 18"

Engine rated at 3000 rpm, 2.57-1 gear.

Runs to 2900 at WOT so will probably take out 1" of pitch or remove some blade area from the blade edges. I'd rather increase blade loading over decreasing pitch. My MP prop cost $700.

Did I show you these pics of the Vashon at Ketchikan? ...
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Old 10-20-2013, 06:47 AM   #15
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Runs to 2900 at WOT so will probably take out 1" of pitch or remove some blade area from the blade edges.

WHY? do you often cruise on the pin at 2800-2900 RPM?

If you cruise any slower than that there is zero reason to change.
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Old 10-20-2013, 07:56 AM   #16
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Thanks for the pics, Eric. That is definitely a salty Vashon. I know they came in two flavors--one with the engine in the fish hold (mine) and the other with the engine in the wheel house leaving the fish hold open.

I tested the prop yesterday. We left St. Petersburg and took the boat to Pass-a-Grille. First, please ignore my numbers in the last post--I must have misread my log or perhaps I can blame old age. Anyway, here is my informal report:

- Old 16x10 prop gave me ~3100 RPM (probably was closer to 3150) at WOT. New prop 16x8 (same make/model) gives me a WOT of almost exactly 3600 RPM. Volvo states WOT should be 3200-3600 RPM.

- Volvo's recommended 300-500 RPM below WOT as my "cruise" is rather noisy and just doesn't "feel" right. I was happy, my wife was happy, and the boat seemed happy cruising at 2800-2900 RPM (about 80% of WOT).

- I occasionally cruised at 2600 RPM (my old cruise with the 16x10 prop), which gave me around 5.2-5.4 knots.

- Speed was all over the place because of weather and currents. At 3600 RPM, I topped out at a speedy 7.2 knots at one point. Cruise (2800-2900 RPM) averaged around 6 knots, but we probably ranged anywhere from 5.5 to 6.3 knots at cruise.

- No more excessive prop walk.
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Old 10-20-2013, 09:53 AM   #17
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OK but you seem to be perfectly set up now too.

"- Volvo's recommended 300-500 RPM below WOT as my "cruise" is rather noisy and just doesn't "feel" right. I was happy, my wife was happy, and the boat seemed happy cruising at 2800-2900 RPM (about 80% of WOT)."

Isn't happiness great? That should be about 50% load (about exactly the same as me) and that load seems adequate for temps and all.

Yes I think reductions in pitch always reduce propwalk. Imagine the extreme of low pitch .. no pitch at all. And w no pitch there wouldn't be any propwalk at all.

How much rated power on that volvo? Three or 4 cylinders?
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Old 10-20-2013, 10:23 AM   #18
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Yes, I most pleased with my current prop. It took a couple of tries, but she's nicely set-up now. My Volvo has three cylinders and crankshaft power is 29HP. I'm looking at the curves on my engine and peak torque is at 2400 RPM. Calculated propeller load at 2900 RPM (my typical cruise) appears to be over 50% (52.6%).

On a somewhat related note, Sherpa was originally powered with a 18HP Saab diesel. Based on how I use my trawler (e.g., Tampa Bay and Gulf of Mexico), it is nice having the extra HP to handle currents, wind, and bad weather.
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