Re-pitching/ replacing prop on Seaweed

Janice- I ran your numbers on the Boatdiesel calc: 20'wll, 7000lb, 15hp@ 2200rpm, full displacement, 1.9:1 gear, 3b prop. Came up with 15" dia, 10.4" pitch.

I think you would do ok with 15x10, 16x10, 15x11, even 16x11 or 15x12. Look for 3b 1.250"bore. Not sure of your gear, you mention left hand, and if I remember the old Volvos there is a preferred direction of rotation.

I would not go down to 14" dia. Gettin pretty small there.

Ski in NC

14" dia = small?

Remember the 15hp part?

manyboats said:

Ski in NC

14" dia = small?

Remember the 15hp part?

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Yep, but it's a 2200rpm engine with 2:1. Need some diameter to push on the water. 14 will push it, but slip will be high especially at lower cruise rpm. 15hp is small, yet the boat is 7000lb. This is a little out of my element, I usually deal with hundred-odd hp. Not 100% on this one.

At this point we don't know if the propeller is good (do you know how to test one?)

The only way to check a prop is for a prop shop to put on a bench and check the blades with a pitch gauge .

Usually hunk of wood with the proper shape that fits the pitch, yes they usually have dozens.


AS a simple rule of thumb at 1000RPM shaft speed an inch of pitch is one K thru a non slip material.

So at 1000rom a 10 inch pitch would give 10K if the water were mahogany.

With 50% slip the 10K becomes 5K about right for this size boat.

IF the boat is lighter , slimmer and with a smooth bottom the slip might only be 40% , so closer to 6K might be observes underway.

Tied to a dock , at zero speed the engine will overload if the prop has enough blade area.

Ski and FF,
Good points.
I wondered for years why Willard didn't put a 3-1 gear on the Perkins and a 20-21" prop. There's plenty of room. Don't know any repowered Willard 30 that has a bigger prop either. If I haden't kept my 2.57-1 BW gear I probably would have done it though.

But I think I understand the prop issue better now. Too much pitch and you get more slippage as the water tumbles out and around the blade tips. Thrust is lost. Too much diameter = too much blade area (unless you have a very unusual prop). At some point of increasing the dia most of the power will be eaten up just turning the blades through the water and all that blade area and nice low pitch won't have the power to push much water.

A square prop (same pitch & dia) will have too much slippage for a slow boat like ours. A prop w half as much pitch as the dia takes too much power to turn the prop and all that blade area so it produces less thrust. Seems to me I read somewhere that a prop w 3/4 as much pitch as dia has the best balance of tip losses and blade area drag so the most efficient prop lies in this pitch/dia relationship. A 20" prop w a 15" pitch, a 16" wa 12" pitch .. 24 X 18 ect. This is not to say that a 24 X 12 prop is unusable but it's less efficient.

Also a very low pitched prop would probably have more thrust at WOT and zero speed. Best for giving that 80' yacht a tow back home. With a little more pitch it would probably be best for top speed on a trawler. And w more pitch yet it would be optimized for cruise at 60% load and more yet best for cruise w a 40% load ect. The thrust cruve is steeper for low pitch and flatter for higher pitch. That's why you can put an 8hp OB on any boat and go wide open throttle. The prop has lots of slip at all speeds and therefore is very flexible.

So I think the ideal trawler prop is about half way between a square prop and on w 1/2 as much pitch as dia. People tend to feel a larger prop will have more thrust so tend to lean in that direction. So many trawlers have a little more dia and less pitch than would be optimum.

Northern Spy said:

Call vicprop. They have a huge stock of used props that they will repitch for you. They did mine for my repower.

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You know Northern Spy, that's a marvelous idea. I've taken it.

Of course their computers are down today -- it's a bit hectic there I'd imagine.

But yes, they provide the calculator and if the price is close, that's what I'll go for. Used are all over the place, and the quality at least from the pictures, it would cost $$$ to recondition.

The estimate from a shop down by Tampa, with re-boring from 1.125 to 1.25 was $200 - $250. Plus shipping every which way, the cost of used... well, unless VicProp can come up with a used propeller (I'd trust them), well, I'll be dropping $500 for a new one.

Painful, but this is a one time outlay so...
I've seen a couple of online buys (here at the mechanic's) and they were ugly. It's put a bit of fear in this purchase -- a real prop company's used offering would be trustworthy. Otherwise, well, not so much.

What say the experts? This is new territory for me......

I wondered for years why Willard didn't put a 3-1 gear on the Perkins and a 20-21" prop.

Probably to keep the engine from under loading.Keep down noise and have a longer service life.

Far lower piston miles.

The HP available changes with RPM, so operating at 3000RPM for cruise rather than sat 1500 will place the engine in a far more lightly loaded regime.

DIESEL Engines like to be well loaded and a boat that will cruise at minor HP needs to be geared to obtain a good load at cruise RPM.

IF you towed 1/2 mile of net probably 6-1 would make sense..

Fred,
Didn't have anything to do w overpropping or engine loading.

I assumed propping correctly to rated rpm whatever the prop size or gear ratio. All the rest I've said so many times I'm not going to repeat it.

The engine loading does have consideration too. I know in neutral 1910 is WOT, but the "sweet spot" (noise and vibration) is 850ish. But that's in neutral so today she leaves the dock for a test run with the newly cleaned manifold. A spin will be nice.

I've got to bleed the system and reattach the tank. Was running from a 1/2 gallon jug of fuel versus the tank. I filled 'er up Monday morning at 3.39 (shrimp boat price) so that was lovely. $125 is silly, isn't it? And that (provided Bob is right) will give me a range of 700 miles: 500 practical. We shall see.

Life is great afloat. And I'm happy. The shrimper had me blocked in (big boat) but now I see river and want to be there.

Thanks to all for hand-holding and advice. I've learned a bit and am hoping VicProp can fix me up.

Janice, if boat runs nice at 850 and engine does not smoke, I don't see any harm running it there with existing big prop.

Also, if engine only goes up to 1910 no load and makes 1900 at full load, that sure does not sound overloaded. Double check full power numbers with your new tach.

Searching for a better prop might be a challenge. 15x10 or so is too big for skiboats, too small for most larger powerboats. Uncommon size.

But it is worth it to check prop shop prop piles. All shops keep old wheels around, and rarely advertise. When I needed a prop, I planned a car round trip to visit several prop shops in a 100mi radius. One shop had a nice one exactly what I was looking for, at about 1/4 the price of new. Put it on and rpm/speed numbers were magically dead on.

Enjoy the run and let us know how it goes!!

VERY VERY good point Ski,
From her reports that's probably the case.
Missed that one.

2200rpm rated power point is a very low rpm for a small engine. I would think it would be about 3000 or 2800 to 3600.

Found, purchased and delivery this weekend or Tuesday. [14x12 being re-shaped to 14x10.]

Next, haul, swap props, plug the two exhausts and then except for test runs (lots of those) I'll be on my way. Using the boat... what a concept, eh?

Life is great and I'm so happy I'm almost bouncing. Of course that might be because of Ray Stevens on the radio. I love that squirrel song.

All sounds good Janice. Keep on bouncing.

Eric - the early 1970's MD-1 & MD-2 volvo's are slow revving, 2000 -2300 rpm.
The later 80's vintage such as my MD17 are good for 3000 rpm.

Janice - Here's a MD-2 workshop manual, in case you don't have one.
Boatinfo - Volvo Penta MD1, D1, MD2, D2 Service Manual

Regardless of the RPM most diesels will live longest at 1HP / 3 Cubic inch of displacement.

Higher RPM increases HP and the wear rate.

If I remember the MD 1 is about 30 inch disp so shoud run >forever< loaded to 10 or so hp. 1/2 GPH or less .

IF the boat goes at a realistic speed (5+K underway) at 850 RPM I would think the existing prop is fantastic. Even if 1200-1500 is needed its about right.

For folks that need minor thrust (under 25- 40 hp) IF the boat has the room a 2 blade will frequently be a better choice than 3 blade.

The opening diameter will need closer to 20% prop diameter as tip clearence if the hull is lightly built , to not make noise.

The blade area must be sufficient for the HP.

On our 90/90 the prop is a 19/13 TWO blade , but with a narrow blade from a motor boat prop , not a really skinny sail prop. Nice low induced drag.

This is efficient 3/4GPH at 6-6.5K ditch crawling. MD 3B / 18,000 LB Disp at full load.

And of course when locked in its indexed location , there is almost no prop drag from form , just from the surface area .

Skeens Elements of Yacht Design is the place for watching the changes wrought be wider blades , larger diameter , or changes in shaft speed.

Update: The new 14x10 prop was installed last week and she moves very nicely. Seaweed has absolutely ZERO wake. Nothing. Doesn't matter if I'm doing five or less -- there's just ripples aft.

Sweet.

Her "sweet spot" is 4.4 and she must moves through the water so nicely. I'm beyond delighted.

Was "set" to leave in the morning but alas, forgot to bring the propane down to the boat and it's locked up. So, leaving when I get it. The bilges are stocked and we are ready.

Paper charts laid out and the newest version of OpenCPN installed. It's better incidentally. The old version would sometimes lose the GPS puck. This one, when that happens you can simply shut down the USB port, then restart the USB. The older version required a restart of OpenCPN -- this is a big improvement.

It (OpenCPN) also has AIS built in -- if you've got a way to receive the signal, it will display. Looked spiffy, though I don't have one of the gizmos. Just in case you wondered.

Has tides and more. I think it's nifty and frankly, the Help File is one of the best I've ever used. That's why I donated. (OpenCPN is free, but they like donations of course.)

Life is wonderful afloat. I'm so fortunate -- truly blessed.
And my new engine? Well, I could not be happier to finally have a sweet little diesel.

Nice to hear it all worked out.
Bon Voyage!

Best of luck on your new diesel power unit and your voyage, keep us updated.

Where you bound for, Janice?

jwnall said:

Where you bound for, Janice?

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I was taking advantage of this weather window we've been having. Since a week ago Friday (day ten and counting) one to two foot seas for the Gulf of Mexico. Truly, it does not get much better.

BUT I took the advice of an expert. When we ordered the two fan belts for Seaweed (she's got a starter/generator) I asked about ordering a second pair "just in case" and was assured that these belts do not break.



Well, as you can see (isn't hindsight always 20/20?) the bracket is slightly cocked and that torque caused the front belt to become loose. I have a turnbuckle aboard and was able to wedge between the place where Hercules could crank her (just above the exhaust hose on the left) and the starter/generator.

I tightened her each day.

Then, on Thursday evening while cruising along nicely the engine bogged for a moment. I turned on the auxilary fuel pump and she again ran smoothly. A look in the bilge and all seemed well.

That night I anchored, and all was normal. In the morning there was oil in the bilge -- none the night before -- so I cleared out about a quart and then looked to the engine again. That's when I spotted the fan belt, broken.

This motor requires both to start, so I radioed TowBoatUS. No answer. None, on all three radios. (I knew I was broadcasting because I could hear on the others.) Still, I did what I've never done before and made a "Radio Check on Channel 16" which was promptly answered by SeaTow.

The SeaTow fellow did a phone relay to the Steinhatchee TowBoatUS captain who came for me. I provided coordinates from my log book. TowBoatUS was to arrive by 10 a.m. but one of his two motors quit on the way so actually arrival time was after 11.

Not a biggie for me I was at anchor and life is the same rather I'm tied to a dock or at anchor -- at least when the sun is shining. Sipping cold tea and relaxing with a book...

The trip back to Steinhatchee (there's wifi here) was uneventful and now I'm waiting for delivery of four fan belts.

Side note: Called a car place in St Pete and was quoted $40-$45 each though he had just one in stock. Next tried Grainger in St Pete. Four available for $12 each. Including shipping: $70. Ordered at 2:30 and shipped by 4:30 with arrival predicted for Monday. I'm pleased.

So currently I'm at a dock just past the bridge -- it belongs to a friend of the TowBoat captain and the owner even ran an extension cord for me. I haven't been ashore.

Yesterday I regrouped. Today I'm almost feeling human. And hopefully tomorrow all can be fixed so I can be on my way again. From the picture above it seems apparent the bracket needs to come out 1/4" on the engine part -- some washers should handle that.

Anyway, that's tomorrow. Today I'm relaxing. And when I get done, I'll rest.

Lesson Learned: The next time an expert tells me something that seems wrong I'm going to go with my gut instinct. I KNEW having spare belts was smart and let myself be dissuaded. I won't make that mistake again -- not on purpose anyway.

So John, are you sorry you asked?! I'm heading south -- a stop to visit a friend in St. Pete, and then to the Keys. Beyond that, nothing is certain.

janice142 said:

So John, are you sorry you asked?! I'm heading south -- a stop to visit a friend in St. Pete, and then to the Keys. Beyond that, nothing is certain.

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Nope. Glad I asked. Only thing I am sorry about is that you didn't stop over in St. Marks so that I could meet you.

Sorry to hear about the troubles. Sounds as if you are coping in your usual unflappable style, however, They do say that life is a series of learning experiences. And Steinhatchee is not all that bad a place to spend a little time.

I was concerned that this weather window would collapse. Frankly, I've never (not in 1.5 years) seen ten days of 1 to 2 foot seas for the Gulf of Mexico. And the prediction continues through later in the week. I'd like to get down to Tarpon Springs so that I'll be "inside" for a while.

The boat was running so nicely too.
But I've learned: experts know a lot but sometimes intuition or instinct should be listened to. If I'd had belts I probably could have effected a fix without involving TowBoatUS. The weather is perfection out there too.

Just beautiful traveling weather with fish out the kazoo. What surprised me was that I saw no fishing boats taking advantage of the schools of fish that are literally everywhere.

The dolphin were fat and happy. I even saw a frigatebird. Hadn't seen any of those since Tropical Storm Isaac a couple years ago....

Sorry I missed you and your bride though. Maybe on my way back...

Janice, a couple things occured to me as I read your post about the belt problem:

1. The fact that you could tighten your turnbuckle each day suggests that something was moving as you tightened. The hose-clamp on the starter/generator (Dynastart?) might be the culprit, if that is how the adjusting bracket is attached.

2. "This motor requires both (belts) to start". Forgive me if I'm preaching to the choir, but I believe the levers on the valve covers are compression-lifters. Raising them to the vertical position will allow the engine to turn easily. Move the levers back again to run. Makes life easier for belts and battery. Equally, "Hercules" could hand-crank the engine without raising a sweat!

3. You mention switching on the auxilary fuel pump when the engine bogged, and subsequently finding oil in the bilge. Did you find the reason for either?

Compression relief valves are great to have. In case of an almost dead battery open the valves and get it spinning then shut the valves, or even just one, to fire it off. Can really save the day.

Janice,

Mike mentioned the mounting bracket and I remember it as being pretty substantial. I had a MD-2 in a sailboat long ago. I had to rebuild the dynastart and changed belts a couple of times. I don't know how your belts could be that far out of alignment unless the bracket is very loose, or broken.

I would definitely find out why this is happening. The bracket is mounted over an inspection cover on the side of the block and shares the same mounting bolts. If it is loose or broken, you could be losing oil there.

Hello Shoalwaters. Yes, you're correct about the compression levers. Both raised to start, then lower aft one first when RPMs are up, followed by front when the engine catches. She will start without that process however, that's the way I was advised to crank her up.

The fellow was here. He shimmed at the bracket versus engine side. Several washers moved it out a bit and now it looks better.

The oil leak was one bolt on one of the two inspection plates on the starboard side under the starter/generator. It was loose. Vibration -- after all, she is a diesel.

I think all is well and after I re-up my oil supply I'll be leaving in the morning. At least the next day will be without cell phone coverage so I'll be missing my imaginary friends. (That's y'all.)

Later today I'll chase down the owner of this dock and pay him, then go anchor for the night. No need to pay dockage now that she's fixed.

The fellow who fixed her was a gem -- very professional and not too $$ either. He arrived with tools to do the job -- had been here earlier to look at the problem and a reasonable price fixed everything. I'm pleased.

Am anxious to be underway. The weather window is still open (1 to 2 foot seas in the Gulf of Mexico) so I want to take advantage and get further south ASAP.

Life is wonderful afloat. Off to re-fill the water tank and toss the trash. I found a dumpster when I went to pick up the new belts.

Me.

Shoalwaters said:

Janice, a couple things occured to me as I read your post about the belt problem:

1. The fact that you could tighten your turnbuckle each day suggests that something was moving as you tightened. The hose-clamp on the starter/generator (Dynastart?) might be the culprit, if that is how the adjusting bracket is attached.

2. "This motor requires both (belts) to start". Forgive me if I'm preaching to the choir, but I believe the levers on the valve covers are compression-lifters. Raising them to the vertical position will allow the engine to turn easily. Move the levers back again to run. Makes life easier for belts and battery. Equally, "Hercules" could hand-crank the engine without raising a sweat!

3. You mention switching on the auxilary fuel pump when the engine bogged, and subsequently finding oil in the bilge. Did you find the reason for either?

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For future reference, once started, is there a reason not to run the engine with just one belt? Or none? Does that belt system have anything to do with the water pumps like on my old Beast?

You'd also asked about the hose clamp -- nope. The yellow arrow is the adjustment point I was messing with. I've got a turnbuckle that the forked end fit on the starter/gen brace (just below where the bolt goes through)

There are two bolts at the bottom but I didn't touch them.
My turnbuckle went from the pivot point (top yellow arrow) to the place where the hand crank attaches. I used a block of wood on the crack part so I could get a good wedge in there.

It would have been better to use a long pry bar. I have a piece of stainless tube I could have used but the turnbuckle was handier -- and I'd had to use it with the Beast as the belts stretched.

According to Calder, up to the first 100 hours belts stretch. And mine certainly did on the Beast. I hated that monster and learned way more than I ever intended to about it.

Thanks Larry - you were right about the inspection plates. The aft one, center bolt at the bottom was not tight. It is now.

It's a dead simple engine. The alignment for the starter/generator was difficult -- no brackets came with the engine so the ones I have were created. It looks better now.