How much HP will a certain size of propshaft take?

MYStargazer

MYStargazer

Well-Known Member
Joined
5 Jan 2006
Messages
1,379
yachtstargazer.wordpress.com
Further my thread on re-engining (or not) - thanks again for the thoughts, chaps! - I wondered if anyone knew of any resources to calculate the maximum hp a propshaft of a known diameter will take.

Mine are 2" in diameter, and look beefy enough to take anything. I'm looking at 320hp Ford Sabre versions of my boat's current Ford Dorset/Dover straight-6 Ford Thorneycroft (150hp)...

I dream of being able to make the old girl semi-plane properly...

Thanks, peeps.
 
What the shaft will take is a question of torque, not power, strictly speaking.

Depends on material, but assuming it is a high strength stainless like Temet, a 2inch shaft will take 320hp at normal rpms. That would be pretty much a normal set up I reckon
 
speak to Paul Williams at www.clementsmarine.co.uk but I am confident that your shafts will be fine, what gearboxes have you got, if they are borg warner as I suspect 1.1's then they will not be man enough for the proposed power upgrade. The most they will take is 212.
 
Have you considered the fuel consumption of two 320hp engines?? It may well frighten you. Also the 320's are getting very stressed, remember these blocks were not really designed to go above 250hp, I would also see how much they will cost you. I agree with Omega2, the shafts are good for 212, I would go with them, if you really feel the need, but by the time you have new engines beefed up the mounts, etc etc. Might be better to get another boat!
 
Sabre built some fine engines out of Ford Industrial Dover base engines. For the higher ratings Sabre even had their own blocks cast. However 320/350/370 were not great engines, even in their time.

However the engines you are being offered are WORTHLESS. When Catapillar finally absorbed Sabre they scrapped all spares and support for these motors, absolutely everything!

If you have a piston go which is not unknown, there are none out there. Special for Sabre. Once over 250 ratings the the Freemans put many bespoke components into the engines contrary to peoples understanding they are not just hand built Ford Dovers.

Another example is main bearing caps, not the cast Ford item it is a steel forging. They still fail despite being a steel forging. Supplies of these dried up even before the scrap man arrived.

Seriously do not even consider the Ford Sabres. Mermaid can give you support up to 250 after that these engines are just a money pit.
 
The high HP engines, were not really designed as pleasure boat engines, more for the diesel racing crowd, not very reliable and went bang frequently. Like I said, 250 is about max.
 
At a rough guess with out either of the books I rely on for this sort of thing I'd say 2 inch is fine.

I know of a couple of boats running those big Sabres with smaller than 2 inch shafts. One boat is 1:1 and the other is 1.5:1

Those engines run the two stage charge cooler, I have heard of them suffering and I suspect replacements are either not available or equal the national debt of a reasonable sized country!

The main bearing cap problem with them is well known and they are V thirsty.

I suspect that they are relatively cheap, not many people want them now as they are long in the tooth and as others have said support is poor. If you really really really want this pair then wind the fuel pumps down to 250 or 275 for longevity.

You need a 6 litre slogger for your boat, you should be looking at Perkins Phaser, marine badged as M185 up to M300Ti (although watch out as hp ratings are a little misleading, the M300Ti is in fact a 260 hp motor). The other top choice would be any of the 5.9 BT cummins. Would be well worth talking to Mermaid in Ferndown about newer Fords.

And most important of all (there I go again starting a sentence with 'and', my english teacher will be spinning in her grave) the Fords do sound best!
 
By the way, I have two 135hp mermaids (Fords) in Englander and swear by them, excellent engines, no turbos, I like naturally aspirated engines, much simpler.
 
shaft.jpg

is that OK?
 
You must log in or register to reply here.

Share this page

Top