propeller shaft bertram

Bonjour,

Is there a good professional in Thailand for give me an advice for put a bigger
propeller shaft on my bertram 42
I am on the koh samui side and look for professional technician and yard able to change prop saft by a bigger one then buy a pair of good propellers

thanks a lot

pascal

 

Hi pascal, may I add the mail you sent me to give the technical data:


> > Hello
> > i hope i dont bother you
> > you looks like knoing a lot about propellers
> > and i got a problem as i live in thailand and could not found any
> > real professional there or anybody i could belive i am looking
> > around on the web
> > I bought an old bertram 42 datas as follow bellow
> > I got horrible local 22 inches prop which doesnt work at all very
> > low speed big fuel consumption huge water move right at the back of
> > the boat, big vibration and noise ect.......
> > I would liçke to change the prop for 28 or 29 good Veem or Hung
> > shen MVP 5 blades but my shaft are only 1.75 inche so small for 325
> > hp and 2-1 gear box
> > could you said me how to change my shaft and which propeller better
> > to buy for an old boat of 1984
> > could i change the shaft easy without costly work and could i do it
> > myself did i got to touch too much the hull for go to 2 inches
> > shaft for exemple or even 2.2 what are the part to chan ge with
> > that if you dont know did you know somebody with reliable advice I
> > am a little lost at the end of the world with my tecnical works
> > Thanks a lot
> > kind regards
> >
> > pascal
> > datas there after
> > - dry weight 19 000 kg
> > - Weight in charge 21 200 kg
> > - total length 12.95 mètres
> > - lwaterline length 11.50 mètres
> > - beam 4.23 metres
> > - waterline beam 3.85 metres
> > - draft from mini 0.83 metre to 1.22 metre maximum
> > - Hull 17 degre deep V
> > - Bridge clearance 17.11 pieds
> > - From the prop axe to the hull 48 centimètres
> > - Twin engines détroit diesel 671TI in ligne with compresseur TURBO
> > et INTERCOOLER des injecteurs de 90 pour une puissance de 325 hp
> > par moteur
> > - Le model 6-71(1062-4310)serial 6A287260 PORT et 6A287354 STBD
> > - transmission Allisson manufactured by detroit diesel Allisson
> > Ratio transmission 2.1
> > serial 42708 numero 6770016 PORT M20Ra et STBD serial 42416 numero
> > 6770015 M20L
> > - propeller shaft 1 pouce 3/4
> > - RPM cruising speed 2000
> > - Maximum RPM 2300 WOT
> > - RPM transmission in neutral 3000
> > - IDLE range RPM 500/900
> > - Governor type SW.VS
>

Regards
Richard

 

Mmmhm, see what you mean, Richard. This lady is really sitting down with a heavy load on her bottom. Any chance to get rid of some of that overwheight in the first place???

Preliminary calcs would point to ~20 knots with the available power and a shade of a margin for sea state. Props would be something like 4 blade BAR 0.7, D 28", P 26". Might have to fiddle those figures slightly, depending on shaft angle and bracket arrangements, but pretty close...... To make this complete, a calc of hump conditions is a must with this fat lady.

Think that Mikado propellers should be represented in the region; I have found them to be good value for their cost.

Shaft should be 50 mm, provided AISI 429 or equivalent could be available. Maximum free shaft length ~2000 mm.

Please note that all figures above are preliminary and subject to uncertainties due to lack of full info!

So Richard, can you find a decent yard for the swap among your contacts???

 

Hello,
This boat is very heavy for it's dimensions and getting over the hump will be a problem.
One info is missing: is it possible to know the distance between the propeller hub and the hull plating? If it is a case similar to one I saw recently (not a Bertram, though) I have a suspect that the maximum prop diameter to be considered will be limited by the hull geometry and maybe you will not have the luxury of having enough space for a 28" prop. The propellers will be heavily loaded and cavitation needs to be seriously considered, imho, both over the blades and between blade tips and the hull.
Pascal, if you have already considered that when choosing to go after 28-29 inches prop, I beg for pardon.

 

Thanks Baeckmo and Daiquiri!

I have no contacts in Thailand in our business, but hope Alik will chime in.

 

Thanks to all of you
I got 48 cm under the hull so i thinks it is easy for big prop
I will get a bit lighter when i will have repared my oman generator but here spare part difficult to found and very expensive.but i will be a good diet for the Lady.
I will need 50 mm shaft ? it is big ???? or there is there a good security margen
anyway thanks for your help oh i forget what mean hump condition

kind regards

pascal

 

Yes 50 mm sounds to be right with the usual safety margin.
Going over the "hump" means the transition from high displacement speed to planing speed. Once the boat is planing it needs less power to continue planing than it did need to come to that speed. Whith a wrong setup it might be possible that you cannot leave displacement speeds at all.

Regards
Richard

 

Concur with the above.
You have around 34 hp/tonne (not a lot)...which according to my charts and for this 'type' of boat will get around 18~19knots, as a rough stab...so this tallies with Baeckmo's too...and as Richard has pointed out, you may even struggle to get over the 'hump' to start with

 

Did it help if we give trim table more angle ???

 

For installation/parts, contact these guys: http://www.candc-marine.com/
If You need help with prop calculations, we can do it. Or Mikado will do it as well - but for free

 

Hmm, there are times I really like you guys.

No, get rid of the weight, and install a proper prop. Then we will see further.

 

Mmmm I got 35Hp per ton and I cruise at 20,
I don't know max speed but i've seen 23 on the GPS.

And im semi displacement.

There is no one in Ko Samui, that is a tourist Island,--thats a very bad choice of place to repair a boat. You can get any shaft or prop you want by driving across to Phuket or Crabi, or possibly Chumpon, Surathani and Hadyai

 

Frosty

Based upon limited data (ie lines plan and shaft/prop dwgs etc), one can only err on the side of caution when providing figures. I have curves for various hull forms each slightly different, giving different "expected speeds". The fact that there is just a few knots difference is indicative of that.

For example...is your shaft/prop arragement the same as Pascals?..Is your boat also with an L/B of just 3?...and so on.

 

I designed and built my own surface drives which are not supposed to work on semi displacement according to architects.!!!! Sorry mine work perfectly.

I prefer the total Hp divided by the sq root of the length divided by K which is the performance of the drives. 2.5 is normal
As you can see mine come out at 3 which is excellent.

I am creeping up with speed year by year making alterations to rudders etc . But Im not an architect so WTF do I know. Don't listen to me.

 

thanks to all of you

I will contact that adress of Alik and see where they can operate
on my side of thailand very few shipyard knowing about this type of boat
whit my wooden junk boat i alway go to Chumphon or Khanom let see what
Alik adress said me,
For calculate prop size and pitch what type of extra data did you need ???
Nice to have you with me
Kind regards

Pascal