Propeller replacement calculations – please help me!

MYStargazer

MYStargazer

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A few weeks ago, my props and prop shafts were nicked less than 48 hours after I removed them from the boat for safekeeping (http://www.ybw.com/forums/showthread.php?357793-Stolen-in-broad-daylight!).

Now it seems that the contents insurer will pay for replacements. Great. Trouble is, the sizes were stamped on the back of the props, behind the nut which I hadn’t yet taken off. So I don’t know exactly what size they were. I’m going to have to work out their sizes from scratch.

Here they were on my boat http://myfitzroy.wordpress.com/2013/04/26/pulling-the-rudders/

And here’s the boat herself http://myfitzroy.wordpress.com/weymouth-32/

I’ve used the Propellor Calculator programme from Castle Marine, and this programme http://www.vicprop.com/displacement_size.php, but the results are not the same.

Does anyone have access to proprietary software, or the one on boatdiesel.com?

Crucial specs:
Hull type: semi-displacement
LWL: 30’ / 9.15m
Displacement = 8000 Kg
BHP = 2 x 180 @ 2,600 RPM
Gearbox = 1.52:1
Maximum speed = 25 kts (but aiming for 18 kts with that Hp)
 
Thanks, guys. I'm guessing the suppliers will carry out their own calculations to make sure they sell you the correct props.

I came across these guys Axiom Propellers (http://www.axiompropellers.com) - interesting looking design. Anyone got experience of these types of props? I'm at a loss as to why anyone would want "equal thrust in both ahead and astern" as claimed...
 
Designed for displacement boats. Not made much headway in yachts. Such tests as have been carried out show little improvement if any over conventional props. Reverse performance more important in low powered yachts and the lack of twist in the blades means the same thrust in both directions. However, similar results can be achieved by having a feathering prop that has different pitch in forward and reverse. This design seems to have some benefits on low speed, low power applications such as narrow boats.

So, probably not a lot of use in your application.
 
Fitzroy said:
A few weeks ago, my props and prop shafts were nicked less than 48 hours after I removed them from the boat for safekeeping (http://www.ybw.com/forums/showthread.php?357793-Stolen-in-broad-daylight!).

Now it seems that the contents insurer will pay for replacements. Great. Trouble is, the sizes were stamped on the back of the props, behind the nut which I hadn’t yet taken off. So I don’t know exactly what size they were. I’m going to have to work out their sizes from scratch.

Here they were on my boat http://myfitzroy.wordpress.com/2013/04/26/pulling-the-rudders/

And here’s the boat herself http://myfitzroy.wordpress.com/weymouth-32/

I’ve used the Propellor Calculator programme from Castle Marine, and this programme http://www.vicprop.com/displacement_size.php, but the results are not the same.

Does anyone have access to proprietary software, or the one on boatdiesel.com?

Crucial specs:
Hull type: semi-displacement
LWL: 30’ / 9.15m
Displacement = 8000 Kg
BHP = 2 x 180 @ 2,600 RPM
Gearbox = 1.52:1
Maximum speed = 25 kts (but aiming for 18 kts with that Hp)
Click to expand...

Can you provide a little more.....

Make of engines, James & Caddy usually fitted Ford Dorset 180's with rated speed of 2,450 not 2,600 rpm.

Need your propeller aperture size i.e. from middle of taper to nearest point on the hull.

Are you sure about 8 tonnes displacement? Is this accurate slinging weight or just a spec sheet #.

Give me the accurate details and I will work it out long hand for you using Crouch's method

Plenty of propeller suppliers out there, Clements are OK, however they tend to over-prop and always potential for engine damage.
 
Latestarter1 said:
Can you provide a little more.....

Make of engines, James & Caddy usually fitted Ford Dorset 180's with rated speed of 2,450 not 2,600 rpm.

Need your propeller aperture size i.e. from middle of taper to nearest point on the hull.

Are you sure about 8 tonnes displacement? Is this accurate slinging weight or just a spec sheet #.

Give me the accurate details and I will work it out long hand for you using Crouch's method

Plenty of propeller suppliers out there, Clements are OK, however they tend to over-prop and always potential for engine damage.
Click to expand...

Cheers, Paul

It's Benjamin - I've just changed my username to match the boat's name and my new blog. I'll put a link to your Cummins Project blog on my blog shortly...

Yes, it's a James & Caddy with 2 x Ford Dorset 180's, but I'm going to install 2 x Cummins 6BT from a DAF 130, with the fuel pump tweaked to 150 Hp initially, then up to 180 Hp, or more, as tweaking allows.

Propeller aperture = 11½"
Displacement = 7620 Kg, but I do tend to keep quite a bit of **** on board. This figure was taken from Halmatic's data sheet for the boat.
 
I am surprised at your estimated weight I had a Halmatic 34 (Weymouth) 2x sabre 265 full fuel way and stores weight 8500kg from the crane.
 
Bandit said:
I am surprised at your estimated weight I had a Halmatic 34 (Weymouth) 2x sabre 265 full fuel way and stores weight 8500kg from the crane.
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That's helpful, thanks. 7620 Kg comes just from Halmatic's data sheet for the boat, but I've never had it weighed. Mine takes 800 litres of fuel, but I don't know if this was taken account in Halmatic's figures.
 
Clements every time, what a helpfull company, they just did me some Squadron 58 props and they are spot on pitch wise, revs up to 2300 which is spot on where Volvo say my D12 lumps should and after Paul asked loads of questions he decided on the pitch and they are perfect.
 
mikesyam said:
Clements every time, what a helpfull company, they just did me some Squadron 58 props and they are spot on pitch wise, revs up to 2300 which is spot on where Volvo say my D12 lumps should and after Paul asked loads of questions he decided on the pitch and they are perfect.
Click to expand...

+ and even if they are not quite right, they will be "put" right, next opportunity, every job is logged on the computer and results kept.
 
BT, Clements, Hamble propellers, Teignbridge, they are all good........To a point!

Few basic rules.

#1 They are out to sell propellers based on cost/performance.

BT generally come out on top in terms of cost and their propeller calculator is reasonably effective.

Clements will say BT are rubbish as raw castings are sourced from Philippines and just finished here (not sure what is wrong with that). Clements are original suppliers to major builders and will tell you straight off original spec dimentions by simply quoting vessel model/engines so big thumbs up there.

However Clements are a bit keen to prop on the knuckle, bit of a boat goes better with our propeller than brand X propeller, with no regard to real life safety margin. I have attended meetings where the designers propeller proposals have been described as nothing better than an egg whisk, designer turned out to be correct on trials.

Critical point is that OP has still not confirmed requested data, on the basis of what we have so far will be a matter of garbidge in expensive garbidge out.

Offer was made to provide the calculation, not yet taken up. Once you have some numbers to work with simply a matter of shopping around, listen to proposals compare with baseline calculation and pricing (ensuring identical material spec).

I have had good service from all of the above, but moral of the story is don't go putting your eggs in one basket. Shop around.
 
Latestarter1 said:
BT, Clements, Hamble propellers, Teignbridge, they are all good........To a point!

Few basic rules.

#1 They are out to sell propellers based on cost/performance.

BT generally come out on top in terms of cost and their propeller calculator is reasonably effective.

Clements will say BT are rubbish as raw castings are sourced from Philippines and just finished here (not sure what is wrong with that). Clements are original suppliers to major builders and will tell you straight off original spec dimentions by simply quoting vessel model/engines so big thumbs up there.

However Clements are a bit keen to prop on the knuckle, bit of a boat goes better with our propeller than brand X propeller, with no regard to real life safety margin. I have attended meetings where the designers propeller proposals have been described as nothing better than an egg whisk, designer turned out to be correct on trials.

Critical point is that OP has still not confirmed requested data, on the basis of what we have so far will be a matter of garbidge in expensive garbidge out.

Offer was made to provide the calculation, not yet taken up. Once you have some numbers to work with simply a matter of shopping around, listen to proposals compare with baseline calculation and pricing (ensuring identical material spec).

I have had good service from all of the above, but moral of the story is don't go putting your eggs in one basket. Shop around.
Click to expand...

shop around and still get a lemon?? from my own experience Paul Williams does an excellent job, and as I said if he does get it wrong he will correct it. I know of one that was not quite right, and it was "seen" to. Do these other firms offer such a personal service??
 
omega2 said:
shop around and still get a lemon?? from my own experience Paul Williams does an excellent job, and as I said if he does get it wrong he will correct it. I know of one that was not quite right, and it was "seen" to. Do these other firms offer such a personal service??
Click to expand...

All the companies mentioned offer EXACTLY the same service. Only difference is that most of us can live without the same old P.W. BS which some people are gullible enough to enjoy.

Teignbridge is real world class outfit, had a huge following in the U.S and were running rings around Michigan Wheel which is why Brunswick purchased, however messed them up. Now back out of Brunswick ownership but still have all of their technology and personal touch again.
 
Last edited:
Latestarter1 said:
All the companies mentioned offer EXACTLY the same service. Only difference is that most of us can live without the same old P.W. BS which some people are gullible enough to enjoy.

Teignbridge is real world class outfit, had a huge following in the U.S and were running rings around Michigan Wheel which is why Brunswick purchased them, however and messed them up. Now back out of Brunswick ownership but still have all of their technology and personal touch again.
Click to expand...


You go your way I'll go mine!!
 
Thanks for your thoughts, guys.

My hands are tied a little in as much as I am obliged to ask a reasonable number of suppliers and accept the lowest quote, as this is what the loss adjuster requires. Standards of service are too hard to quantify and objectivise, but I'll be choosing the supplier with the best service and paying extra myself if need be, following settlement.

Latestarter1 said:
Critical point is that OP has still not confirmed requested data, on the basis of what we have so far will be a matter of garbidge in expensive garbidge out.

Offer was made to provide the calculation, not yet taken up.
Click to expand...

Matters are made a little more complex as I’m in the process of removing the Ford Dorsets with 2 x 180hp, and replacing with 2 x Cummins 6BT with 180 hp at 2,600 rpm. The only figure I can’t provide with 100% certainty is the real-world displacement. I only have the manufacturer’s figure for this moulding, but this does not take account of the heavier aft-cabin set up and large fuel capacity. But, then, the Cummins are lighter engines. So I've settled at 8,000 Kg.

There'll be time in hand following settlement but before purchase to make any tweaks to the calculations.
 
Most modern mobile cranes will give a reasonably accurate weight which should be about +/- 5%.

You will need a crane or a hiab to remove the engines at the time they need to come out anyway so you could lift the boat at the time to estimate the boats weight taking careful note of fuel water and other stores, then put it back on the blocks and remove the old Ford engines.
 
Fitzroy said:
Thanks for your thoughts, guys.

My hands are tied a little in as much as I am obliged to ask a reasonable number of suppliers and accept the lowest quote, as this is what the loss adjuster requires. Standards of service are too hard to quantify and objectivise, but I'll be choosing the supplier with the best service and paying extra myself if need be, following settlement.

Matters are made a little more complex as I’m in the process of removing the Ford Dorsets with 2 x 180hp, and replacing with 2 x Cummins 6BT with 180 hp at 2,600 rpm. The only figure I can’t provide with 100% certainty is the real-world displacement. I only have the manufacturer’s figure for this moulding, but this does not take account of the heavier aft-cabin set up and large fuel capacity. But, then, the Cummins are lighter engines. So I've settled at 8,000 Kg.

There'll be time in hand following settlement but before purchase to make any tweaks to the calculations.
Click to expand...

OK all makes sense now.

Replacing Dorset will give you a a weight advantage of at least 250 kgs.

Supply me with your total aperture, centre of of shaft taper to hull and I will do calculation for you.

All of the companies mentioned in this thread should give you competitive quotes.

Anything else you require on the Cummins, installation data just PM me.
 
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