Need B31 prop advice.....

IRGuy · Post by **IRGuy** » Aug 16th, '10, 07:07

Hello all...

I received the following message by email.. I am not sure how the writer came to contact me directly, but he needs help with his props after repowering with Cummins 6Bs. It appears to me he is underpropped, but I am wondering if his engines are maxing out their RPMs against the governors stops. Can someone please post some comments to help him? I am writing to him this AM and will tell him to check here for your comments.

Thanks
Frank
-------------------------------------------------------------------------------------

Hello Sir,

I'm the owner of a Bertram 31 in Gran Canaria.
I just replace the old engines Cummins V502 for new cummins 6BTA 330 twin disc 1.5:1 with new shaft 45 mm and propellers 4 blades actualy 20x19.

The boat do after last tries, 20knots but need to do more.The engines need to do full power at 2800 turns but goes to more then 3000 turns.I suppose that's the pitch of the propellers who is wrong?
Can you say me the best pitch for the 4 blades prop.
Thank you very much for your help.

Kind Regards

Louis

Wursty · Post by **Wursty** » Aug 16th, '10, 15:56

i have this exact setup with 6B 330's with ZF trani and 4 blade props and i get 33 knots WOT at 2850 RPMs. i can't remeber the prop size but it seems you are under proped.

bob lico · Post by **bob lico** » Aug 16th, '10, 18:15

i know a little about proping a boat . cummins 330 with 1.5 gears ; nibral 3 blade 21 dia. 24 pitch #5 cup . or nibral 4 blade 21" dia. 23 pitch and # 5 cup.

IRGuy · Post by **IRGuy** » Aug 16th, '10, 19:01

Thanks Bob.. I will ensure he gets this info.

If he can't locate Nibral props, will the dia and pitch specs remain the same?

AndreF · Post by **AndreF** » Aug 16th, '10, 19:54

I'm turning 21X22 4 blade no cup w/250 1993 Cummins - perfect for me.

AndreF · Post by **AndreF** » Aug 16th, '10, 19:58

Nibral is what it is made from, the best, and of course, the most expensive material practical. There are many manufacturers.

bob lico · Post by **bob lico** » Aug 16th, '10, 21:39

yes same for brass.

Carl · Post by **Carl** » Aug 17th, '10, 09:12

Nibral blades can be made a bit thinner, as Nibral is a stronger material. Less thickness is less drag so you may lose some performance with the Bronze counterparts.

bob lico · Post by **bob lico** » Aug 17th, '10, 18:28

andre you notice your 250hp running 22" pitch and mine at 23" with 330hp .the cup affects the use of pitch quite a bit however the total thrust goes up dramatily due to less airated water .effiency will also increase . i have the same fuel burn as 4cyl yanmars at 24 knots.

IRGuy · Post by **IRGuy** » Aug 24th, '10, 08:42

Thanks for all of you who responded with the above information.

It seems that Louis never came here as I suggested, and I relayed the info to him you provided. He wrote back to me saying he could not change his props, but it was unclear to me why. He asked if he could repitch his existing props instead of getting new ones with larger diameter and more pitch. I told him I did not think he could increrase the pitch as much as necessary without significantly weakening the blades, and that he should speak with a prop specialist in his area to confirm this.

He then dropped out of sight without answering my last note.

No thank you, no KMA, no nothing. So much for trying to be a good guy!

CaptPatrick · Post by **CaptPatrick** » Aug 24th, '10, 09:28

No good deed goes unpunished....

Tommy · Post by **Tommy** » Aug 24th, '10, 13:47

Frank,

Although your phantom friend may have dropped out, all of the regulars that come to the Discussion Page benefited from the informed comments. Everytime I click on this page, I consider it a tutorial from some of the most experieced watermen/craftsmen assembled anywhere. Thanks for initiating the dialogue.

Tommy

Harry Babb · Post by **Harry Babb** » Aug 24th, '10, 20:46

We have a Louis as a member on this board......he is the guy that posted pics of a large crane hoisting his boat and positioning it in his yard....then posted pics of a really nice "A Frame" that he used to remove a pair of V-8 Cummins......seems to me that he is in the Mediterranean area around Italy or Greece

Sounds like the same guy to me

hb

luis · Post by **luis** » Sep 27th, '10, 15:32

Harry Babb wrote:We have a Louis as a member on this board......he is the guy that posted pics of a large crane hoisting his boat and positioning it in his yard....then posted pics of a really nice "A Frame" that he used to remove a pair of V-8 Cummins......seems to me that he is in the Mediterranean area around Italy or Greece

Sounds like the same guy to me

hb

Hi to all , and Harry , that Louis is from Canary islands and I am from Portugal , however only now I saw this post cause working times dont let me enough time to read daily. Anyway , I am Luis , the "A frame" guy and my beloved Bertram is slowly getting better. Btw, some months ago I just bough a 1995 Dodge Ram 1500 runing on gas and lpg and its really a nice thing to drive (V8) , I really like V8's. So now I have an american boat and an american truck. I already have the replacing engines for the old V8's - and they are Cummins 6BT-210hp waiting to buy the ZF 45A 1.56:1 - 8Âº gearboxes as advised here on our Bertram encyclopedia.
All the best for all the faithfull

bertram31.com

Need B31 prop advice.....

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