prop size on 260 express

[benjaron]

Hi folks
Curious as to what other's are running for propellers on 260 express
w/ 210 6bt cummins Mine has a 4 blade 18 x 19
Ben

[Mistress]

That's a lot of prop if you have 1:1 gear.

I have 16x17 and it could stand to be reduced. Same thing with a friends HT

The real telltale is what max RPM with medium/typical load do you get?

[Anonymous]

26'CUDDY 210 cummins ,15L16 cupped, cruise2200rpm 24 mph. 2800 27 mph

[benjaron]

Hi guy's
as far as i know i have a 1.3 reduction
Max rpm 2450 @ 29 mph (gps)
cruise @ 2100 rpm @ 23 /24 mph
load has very little effect on performance top speed will drop to app.
27 mph & rev's to 2425 with a full load of fuel & 5 people on board
I think i am as close to optimal as i can get with these specs
possibly a 1/2' less pitch would get the rev's to 2600 rpm cummins
spec but is it worth the effort ????
BEN

[mymojo]

Hey Ben!
I cant remember what prop size was on my 260, probably different casue it had the Yanmar. Are your tach readings accurate? If they are like the tach on mine it read about 200 rpm too low. When the tach crapped out I replaced it with a new Yanmar branded (not Faria) tach and it ran to the full rpm under load which was a good feeling. If your's is reading low you may be over-loading the engine more than the 175 rpm difference suggests. Everything I've read and learned so far about diesels says the most likely cause of early diesel death is over loading. It'd be worth checking the tach accuracy before chasing the prop pitch change.
Hope all is well.
Greg

[Capt Clay]

Hi Ben
I have 250 HP Cummins and my prop is 18X19 four blade, My Top rpm is 2900 with a max at 3000. top speed is 28mph cruise's 23 to 25 mph at 2400 rpm

[benjaron]

Hi capt clay
Obviously from your post the 250 cummins has a lot more oomph than my 210 & it appears you are propped correctly.
The 18 x 19 gives my boat about the same performance as yours but i know i am overpropped. I just installed an aetna digital tach which is supposed to be accurate within 1 rpm My max is about 2540 /2550
which is about 100 rpm better than my original tach which has been sticking. this still is putting me below cummins specs. of 2600 for this engine Optimally i should be running up to at least 2700 to 2750 max.maybe more ???
I may try one of those new michigan dqx props they really looked impressive at the miami show & drop the pitch down to 18" or maybe even 17=3/4 This would certainly take some load off the engine & probably not affect performace a bit Would like feed back from any one who has installed one of these new dqx prop's
BEN

[skipm]

I have the 210 cummins , 15 x 16 cuped, 1 to 1 bw trans. 2200 rpm = 24 mph 2800 rpm= 26 to 28 mph according to load.Max rpm is 2800.

[Scratcher]

Ben; I've been working with Larry at Accutech Marine on re-propping my boat. I just ordered a new Michigan prop, djx series I think. I've been happy with Accutech; they'll give you the projected numbers for your boat and provide an iso class scan of both the new prop and old prop if you want so you know exactly what you are working with. Once I get the new prop I will post sea trial numbers for both the old and new and the numbers in the projection that Accutech provided. Accutech is located in North Hampton NH; I went with them based on the numerous expert posts they've made to boatdiesel.com.

[SCOOTER]

Ben; I've been working with Larry at Accutech Marine on re-propping my boat. I just ordered a new Michigan prop, djx series I think. I've been happy with Accutech; they'll give you the projected numbers for your boat and provide an iso class scan of both the new prop and old prop if you want so you know exactly what you are working with. Once I get the new prop I will post sea trial numbers for both the old and new and the numbers in the projection that Accutech provided. Accutech is located in North Hampton NH; I went with them based on the numerous expert posts they've made to boatdiesel.com.


I recommend that you be very carefull with this prop shop!!

A guy I know that owns a 45' Young Brothers bought a new wheel from them, BIG MISTAKE!! The damn thing vibrated so bad his teeth nearly popped out of his head. The prop ended up being fixed by H&H Propeller in Salem, Ma.

[SCOOTER]

My fathers boat.

Yanmar 4LHA-STE 230hp w/ZF 630A 1.6:1 gear.

Prop is either an 18 x 18 or 18 x 20 4-blade. Not exactly sure which, as it has been stamped twice.

[Scratcher]

Scooter; thanks for the heads up. So far they are one of only a few shops I know that will give you an ISO class scan of your prop. There are so many variables with a prop that this is pretty much the only way to know exactly whats on your boat. After I'd given Accutech the info stamped on my prop they asked me to send it up to them so they'd know exactly what I had, not what was stamped on it. I had to pay the shipping, about $15, but they didn't charge for measuring it. And it was a little different than what it was stamped.

Once I get my new prop I'll post my old sea trial numbers, the numbers that Accutech projected I would get from a new DJX series prop, and the actual numbers from a new sea trial. That will be my measure of success (or failure).

I'm curious about the boat with prop problems you mentioned; most shops when the put a new prop on a boat will tweak it as needed so that rpms and vibration are where they should be, and I know that Accutech does this regularly. Do you have any more details to your story?

[SCOOTER]

Scratcher,

The shop in question is only a few miles away from the marina where I work and we don't & won't use them.

I'm hesitatant to go fully into it here, but I can tell you that the bore in the prop was way out of whack & the blades didn't spin in the same plane.


This is who we use. They've been in business over 50 years, not under 5 like the shop in question.

http://www.hhprop.com/prop.html

[benjaron]

hi scratcher
Curious as to why a 3 blade djx was chosen over a 4 blade dqx are you replacing a 3 blade ???
BEN

[Scratcher]

Ben; Other things being equal, and they rarely are, a 3 blade prop is more efficient than a 4 blades. The widespread impression is that four blades are better than three, I guess because more is often seen as better or because someone had a problem that a 4 blade prop solved and so they think that 4 blades are better in all situations. That is often not the case; rather four blades can solve certain problems like clearance problems,vibration problems, or a where more blade area is needed than can be had in a 3 blade prop. In my particular case the software numbers come up recommending the DJX as being just as good as a DQX and costing less.

If you really want to learn about it there is a good book called "The propeller handbook" by Dave Gerr. I'm lucky that my local library has it on the shelf. Its well written and makes a lot of sense of "propeller science"; which is still part art. If I remember right it is under $25 at amazon.com.

Also, there are online prop calculators at both www.boatdiesel.com ($25 for membership) and I think at the Michigan Wheel website. Members on boatdiesel have said that they have gotten good results from that prop calculator. You'll need to know displacement, waterline length, gear ratio, and engine rpms. Personally, before shelling out $500 for a new prop, I want to speak to a knowledgeable human being.

[benjaron]

Hi Scratcher
You certainly are correct in the controversial world of propellers
At the miami show i had all the info needed to get a prop analysis & i spoke a michigan dealer "general propeller co. & gave him all my info
He got in to a computer & his recommendation was the dqx 4 blade based on the hull design of my 260 exp which he deemed semi displacement with the keel drive. He came up with a max pitch to get the cummins 2600 rpm spec of 18-1/2 " (mine is 18 x 19) @ 2500 + & further recommended i drop to 18" pitch Or a custom pitch of 17-3/4 which theoreticly would top out at 2750 to 2800 rpm His basis was that the increased blade area on the 4 blade dqx was what my hull would perform best with at cruise. He claimed to be very familiar with shamrock" & was a supplier to them
I'm not going to make a change until next fall Which will give me time to pick a few more brains or actually find someone who installs one.
Let me know how you make out & thanks for getting involved in this
discussion
BEN

[SCOOTER]

Scratcher,

Any updates on your new wheel?

[micky692002]

Scooter, I sent you an email. Did you received it? Thanks.

[SCOOTER]

Scooter, I sent you an email. Did you received it? Thanks.

Got it. Will let you know tomorrow.

[Scratcher]

Scooter; I'm still working on replacing my tanks. Had family visiting etc. so its taking longer than I had hoped. I'll post all before and after numbers as soon as I have the the boat in the water and do a sea trial.