1. ## Re: over powering your vessel

I not too fussy anything up to 1950

Originally Posted by cstevens
Given that artif has a Gardner in his boat I'm guessing around 1930...

2. ## Re: over powering your vessel

Originally Posted by artif
I not too fussy anything up to 1950
You may be like the oldtimer. At his 100th birthday party, a well wisher said, "i expect you've seen a lot of changes."

"Yup, I've been against every one of them..."

3. ## Re: over powering your vessel

Am I right in assuming that a particular hull needs a certain amount of horsepower to reach hull speed, assuming no current and smooth water? So if you have the same prop and a more powerful motor, the new engine will use less of its available power to push the hull to hull speed. Correct?

I ask because I repowered my boat, going from about 85 hp to about 110. The new engine gets to operating temperature cruising at hull speed, but doesn't seem to be working as hard

4. ## Re: over powering your vessel

Originally Posted by Bobcat
Am I right in assuming that a particular hull needs a certain amount of horsepower to reach hull speed, assuming no current and smooth water? So if you have the same prop and a more powerful motor, the new engine will use less of its available power to push the hull to hull speed. Correct?

I ask because I repowered my boat, going from about 85 hp to about 110. The new engine gets to operating temperature cruising at hull speed, but doesn't seem to be working as hard
Yes. I suspect artif could give us the formulas here, or I could dig them out of my copy of Skene's, but operating temperature isn't really a good indication of how hard the engine is working. Exhaust temp (EGT) is the best measure here. You could install a pyrometer and get a more accurate indication. And there should be some specs for what the proper EGT for continuous duty should be for your motor. Probably somewhere around 900f.

5. Senior Member
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## Re: over powering your vessel

Originally Posted by Bobcat
Am I right in assuming that a particular hull needs a certain amount of horsepower to reach hull speed, assuming no current and smooth water? So if you have the same prop and a more powerful motor, the new engine will use less of its available power to push the hull to hull speed. Correct?

I ask because I repowered my boat, going from about 85 hp to about 110. The new engine gets to operating temperature cruising at hull speed, but doesn't seem to be working as hard
Check the power curves for your engine, if you have propped it for the correct max rpm, then you can tell how many horsepower you are using by the rpm you are using to achieve a given hull speed. From the rpm you can look at the torque curve and get a pretty good idea of what the percentage of load is.

And the comment on exhaust gas temperature is spot on, it will tell you how hard your engine is working, finding what that temp is for a given engine can be a little challenging. Also, installing a pyrometers gauge to monitor this is a really good idea as it will tell you much sooner then your coolant temp gauge if something bad has happened to your engine, bad like in no salt water flow, because if your exhaust gases suddenly have no salt water being injected into them the pyro will show that instantly, allowing you to shut down before meltdown.

6. ## Re: over powering your vessel

1-Yes
2- Maybe

3- Probably isn't

1- Vessel speed is dependent on amount of effort put in, that won't change, all things being equal.

2- Possibly, but see my earlier post on torque and revs. In extreme circumstances you could be working the engine much harder if the torque curve is mismatched to the prop speed or you have fitted a 1:10 gearbox

3- Given that the new engine is probably similar to the old engine, revs, torque curve etc then yes its having an easy time. As Chris has mentioned EGT's are a good measure of how hard it's working.
Real world, don't worry about it, just change the oil regularly, use turbo rated oil as it has better particulate retention and give it a bit of throttle every now and then to clear its throat.

Originally Posted by Bobcat
Am I right in assuming that a particular hull needs a certain amount of horsepower to reach hull speed, assuming no current and smooth water? So if you have the same prop and a more powerful motor, the new engine will use less of its available power to push the hull to hull speed. Correct?

I ask because I repowered my boat, going from about 85 hp to about 110. The new engine gets to operating temperature cruising at hull speed, but doesn't seem to be working as hard

7. ## Re: over powering your vessel

Originally Posted by artif
1-Yes
2- Maybe

3- Probably isn't

1- Vessel speed is dependent on amount of effort put in, that won't change, all things being equal.

2- Possibly, but see my earlier post on torque and revs. In extreme circumstances you could be working the engine much harder if the torque curve is mismatched to the prop speed or you have fitted a 1:10 gearbox

3- Given that the new engine is probably similar to the old engine, revs, torque curve etc then yes its having an easy time. As Chris has mentioned EGT's are a good measure of how hard it's working.
Real world, don't worry about it, just change the oil regularly, use turbo rated oil as it has better particulate retention and give it a bit of throttle every now and then to clear its throat.
Thanks, that's what I wanted to know. An engineer friend picked the engine and said that swapping the new for the old was a common thing and that the torque curves were about right.

8. Mechanical Engineer
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## Re: over powering your vessel

I call any Diesel Engine with Electronic (Solenoid Actuated and Computer Controlled) Fuel Injectors "Modern",

and Engines with Mechanical Fuel Injection (Injectors open due to pressure and timing in individual line from pump to cylinder, throttle and rpm-mechanically metered) "Old".

"Modern" or "Common Rail" Fuel Injection systems are old new on cars (since 1969, VW 411/412 first production "electronic Fuel injected car), but relatively new to Diesel.

Electronic fuel injection was applied to diesels because the Mechanical Fuel Pumps and Injectors did not have the logic-versatility needed to vary fuel delivery in all the situations it is finely controlled now. Efficiency and Emissions control it. I'd wager exhaust temps are on average higher in "Modern" engines because they are programmed to burn as lean-ly as possible in any given situation, where the more "open loop" Mechanical Systems would have to be set conservatively (slightly too much fuel) to be safe and reliable.

my two cents.

Good article here:

https://en.wikipedia.org/wiki/Electronic_Diesel_Control

9. ## Re: over powering your vessel

Actually there is a push to reduce combustion temperatures and hence EGT's to reduce NOx emissions. Going back to Long stroke engines (old ways work)

But in reality, production engine technology is way behind what is already out there, I was working on VVT cams for Chrysler over 12 years ago, that they still haven't put into production. Why do we even need cams, when electronic valves have been around for years, enabling cylinders to be shut down in low load conditions, just the cheap skate motor manufacturers who don't want to spend the money.
All redundant now anyway, Tesla has put a rocket up the backside of motor manufacturers. More and more cruising yachts are going electric. If I had another life, I would be going for a cat with electric auxiliary propulsion.

10. ## Re: over powering your vessel

More and more cruising yachts are going electric. If I had another life, I would be going for a cat with electric auxiliary propulsion.
Is that really viable yet? I thought there were still major range and efficiency issues? Otherwise I would be seriously tempted to do that in Petrel. I'm going to have to put several hundred pounds of ballast in her to get her down to her DWL anyway. Could just make that a huge battery bank...

But now we are really drifting this thread. Probably need a new one.

11. ## Re: over powering your vessel

Depends on your range requirements, take a look over at Bruce Schwab

Originally Posted by cstevens
Is that really viable yet? I thought there were still major range and efficiency issues? Otherwise I would be seriously tempted to do that in Petrel. I'm going to have to put several hundred pounds of ballast in her to get her down to her DWL anyway. Could just make that a huge battery bank...

But now we are really drifting this thread. Probably need a new one.

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