propeller shaft bertram

[pascal 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

[apex1]

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

[baeckmo]

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???

[daiquiri]

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.

[apex1]

Thanks Baeckmo and Daiquiri!

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

[pascal bertram]

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

[apex1]

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
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

[Ad Hoc]

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

[pascal bertram]

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

[Alik]

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 :)

[apex1]

Hmm, there are times I really like you guys.


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

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

[Frosty]

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

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

[Ad Hoc]

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.

[Frosty]

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.

[pascal bertram]

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

[pascal bertram]

Hello

I am back after 2 months in france happy new year to all of you my best whishes for you and your family in 2010.
I got now time to settle those boat problem and will need advice of all of you experianced sailor, particulary as the cutlass bearing doesnot alowed us to put bigger shaft without glass work is there any alloy which allwed us to stand the power and propeller we want for make those 18/20 knots per hours.
In an other hand could you said me which info you need for make sharpest calculation i dont understand well as english tecnical marine vocabulary i am a begeener.
Thanks a lot to all of you
Kind regards
pascal

[pascal bertram]

hello Baekmo

My best whishes to you and your family in 2010
i am back to my problem and i wonder if there is some alloy performant enought for give me a prop shaft standing the power gear box ration and propeller size able to give us the expected performance of 18/20 knots .
please what more info should i give you for sharper results as you said for going further preliminary

thanks a lot for all
kind regards

pascal

[pascal bertram]

Hello Frosty


As you also live in thailand i wonder if we could some day meet somewhere for a beer ans some talk if it happen to come in samui please be my guest
you can call me anytime on 08 66 82 18 25

kind regards

pascal

[pascal bertram]

dear Apex

Cheers and best whishes for you and family in 2010
Did you think i should try to have calculated the hump condition if yes how
Again thanks for all your help

kind regards

pascal

[powerabout]

A 42 Bertram with only 325 HP is a bit strange?
Inline GM's even stranger

Is it an Australian or American built?

[pascal bertram]

dear Apex

Cheers and best whishes for you and family in 2010
Did you think i should try to have calculated the hump condition if yes how
Again thanks for all your help

kind regards

pascal

[pascal bertram]

hello Baekmo

My best whishes to you and your family in 2010
i am back to my problem and i wonder if there is some alloy performant enought for give me a prop shaft standing the power gear box ratio and propeller size able to give us the expected performance of 18/20 knots .
please what more info should i give you for sharper results as you said for going further preliminary

thanks a lot for all
kind regards

pascal

[pascal bertram]

Hello Frosty


As you also live in thailand i wonder if we could some day meet somewhere for a beer ans some talk if it happen to come in samui please be my guest
you can call me anytime on 08 66 82 18 25

kind regards

pascal

[baeckmo]

Ok Pascal, previously you gave the following info on engines, transmissions and propellers:

Engine power 325 hp @ 2300 rpm. Transmission gear ratio 2:1, propeller diameter 22".

Ad Hoc and I estimated max speed to be ~18 to 20 kn at the best.

What speed do you get with the setup you have today? Do the engines reach just 2300 rpm, or are they overrevving? I would like you to check the transmission ratio once more; is it really 2,0 : 1, and do you have a figure for propeller pitch? How many blades, can you send a picture of propeller?

I'm asking this, because the figures given don't match; either ratio is something else, or engines are running on governor rpm limit.

[pascal bertram]

hello Baeckmo
what i give you previosly was i got 22'' 3 blades prop because the original have been stollen before i buy the boat and we hardly go 12/13 knots but those prop are made here in a factory for thai fishing boat and those prop are moving so much water that it looks like the water is boiling 2 meters after the boat but the boat doesnot move .The gear box ratio is really 2-1 it is what is write on the allison small metal .
we do reach 2300 RPm actualy but at 12 knots with soo much vibrations we definitly got prop undersized shaft may be a bit to long after the strout and anyway undersized for bigger prop. what i have been founding out from the time before my purchase was that at the begeening the boat was 450 HP there where 3X4 blade very tin nibral prop like the occidental makers and after the engine have been put down to 325 HP the Oman gen set gone every stainless or aluminum peaces gone electronic gone ................
I try to found out more but no word on the prop size so i gave up looking for before trying to look for after brings this this boat go 18 knots crusing speed for trying to use it because at twelve knots and 110 liter / hour there is no fun and difficult to afford as i am not a pro from this and as there are no professional around only on the other side of thailand and so little and even less trustable and here a white man with something they call a yacht is suppose to be Rockfeller and i got little to put in that all what i know so i am so happy to have you guys for helping and giving light to my search
thanks a lot
kind regards

pascal

[powerabout]

How much shaft between aft skeg and front of prop?

[pascal bertram]

Hello Powerabout

Sorry I Am French And I Dont Understand Aft Skeg Front Of Prop
A Small Help For Understand My Technical Vocabulary Very Poor
Kind Regards

Pascal

[daiquiri]

Sorry I Am French And I Dont Understand Aft Skeg Front Of Prop. A Small Help For Understand My Technical Vocabulary Very Poor
The distance "C":

http://www.yanmarhelp.com/images/propaperture.gif

(pic abusively taken from Yanmar site... ;) )

[powerabout]

D, actually and keep it under one shaft diameter

If a single 'P' strut (as was standard) you need to be close to help prevent trouble.
The other issue with them depending on the year built, is how strong the hull is where the strut bolts to the hull.

We strengthened quite a few to prevent vibration.

Its a bit of a job as the fuel tank has to come out.

I assume we are talking a FBSF, Fly Bridge Sport Fisherman yes?

( FB Motor Yacht I havn't worked on those)

Cheers

[pascal bertram]

Hello
actualy i dont have this c distance from half the radius to the strut and it doent look like this i will send you one picture and for the d distance i got near 3 time the diameter probably too much for bad and unbalanced prop.
for strengthening it is a kolosal work on this fly bridge sport fisherman and even i was wondering what to do if one day i came to touch and move the strut. got to blow out the rear cabin the tank it would cost a fortune. or may be there is a tric ?
anyway let hope we would not have to strengthening the hull.
kind regards

pascal

[pascal bertram]

40370

here the picture of the prop the strut and the shafts
kind regards
pascal

[pascal bertram]

dear Baeckmo

i have been sending a picture of prop and shaft a little there after
kind regards
pascal

[powerabout]

That doesn't look like the bottom of any 42 Bertram I have ever seen?

There is too much shaft between the strut and the prop so that wont help the vibration problem at all.
Havign a bolt hanging out of the side of the strut to secure the bearing is not great, maybe a grub screw would be better or none at all depending on the type of bearing that is in there.

Do you have a photo of the hull?

[pascal bertram]

Here the boat
kind regards
pascal

[powerabout]

yep that is one
They didnt make the Motor yacht version in OZ so I have no experience with them.
It was the keel that I have not seen before?

[Tigawave]

Performance is also a factor of how much energy goes into shaft bend/whip rather than thrust.

You could try a rigid bearing (I assume you are still using rubber bearings) we have had performance increase reported from users of rigid phenolic composite bearings rather than rubber. Some makes also resist marine growth on the shaft and bearing surface.

[pascal bertram]

hello

could you said me a little more about those bearing rigid
kind regards

pascal

[Tigawave]

When you apply thrust to a shaft it will want to bend, it is the bearings that hold it in place or llimit this movement. The closer you can hold the shaft to a straight line position the less energy will be used up in the shaft bending from its centre line as well as corkscrewing as torque is applied.

If you use a rigid bearing the shaft canm only move as far as the clearance between shaft and bearing surface. Even when running on a water film the shaft can increase pressure in this film as it starts to bend, this increase in water film pressure will force rubber to give allowing the water film to remaain but the shaft to move.

Use a rigid bearing material and the ammount of shaft bend is far less.

There are a number of composite bearing manufacturers I work with one make from Perth which I believe performs better than most if not all of the others. Do a search for marine composite bearings and have a read. They are used in quite a wide range of vessels.

[pascal bertram]

HELLO

i WILL SEE IF I CAN FIND SOME OF THOSE HERE IN THAILAND
ALL THE BEST

KIND REGARDS

PASCAL

[pascal bertram]

dear typhoon

for the hp i am very sure of the 335 hp because i get it out a detroit allison paper with all the details brake hp shaft hp ....
if you give me your e mail i will downloard the form and send it to you with everything official i got pictures ...
i go actualy 16 knots with very bad thailand made junk propellers of 23 inches

thanks for your help if you interested going further send me your e mail
kind regards

pascal coldefy