Discussion in 'Hatteras Yacht' started by Pascal, Oct 15, 2020.
Can we keep the politics off this forum please?
it is the little wooden cat boat. It s covered
We do 9 GPH at 9 kts which is how we run the most. When we repowered we decided to get the 430hp C series to have the option to run faster if needed. Cost difference was minimal.
Looks great ! Very nice and worth the mechanical effort.
Put all those antennas and flags down and you’ll pick up one more knot!
make that more of an Aerodynamic Hatt!
You and Oscarvan have to have a side by side performance race !
I ran a 1979 58' Yachtfish (same hull as pascals with a factory 5' cockpit added) and it had detuned 8v71 TI's with 90 injectors instead of the 110's......it only cruised at 13.5 knots at 1950, but at WOT it did get up and run 21 knots.......it was unstabilized......and sadly the boat rode and ran amazingly better at 21 knots as far as stability went. I always wondered how they'd run if someone put 600HP diesels in them so they'd cruise at 21+ knots, but over the years nobody has that I know of.......
That would remind me of the races I had as a kid. Me in my $10 1960 Ford with blown mufflers and bald tires against my friend in his $100 1961 Rambler. Sounded great with the roar and screeching tires and everyone jumped out of the way as our two hoopties putted up the road getting all the way up to 20 mph in 1/4 mile.
I think it looks very nice at that speed. Great restoration better than it was new. While I like faster, I find that the ability to cruise at 15 to 20 knots is a huge step up from only being able to run at 8 to 12 knots. I think the improvement you've made in your boat is great.
I thought you had used the 550 hp Cummins ?
During survey WOT at 2150 rpm we did 19.2 That was with 1/2 water , 1/2 fuel and empty holding tanks. We've since put "some stuff" on and generally run with full water and 1/2-3/4 fuel...... So I would lose that race. Maybe someday I'll put some big ass motors in it..... Not this week. Next week's not looking good either.
You need to take some pitch out of the props. 2150 rpms WOT is far too low.
Maybe it was in fact 2350. Props are as specked by Hatteras
In 1970??? Boats get heavier as they age, engines make less HP, bottom gets many layers of paint, etc. etc. Not uncommon to have to cut the pitch on the props as a boat ages.
1978. Engines rebuilt 900 hours ago. Bottom is not overloaded. But I will take your recommendations into consideration.
I agree. You re missing 150 RPM and are seriously overloading these DDs
I'm well aware that what you and CJ suggest is indeed the general rule for propping - to the point that engine manufacturers require their dealers to check that a new boat reaches the rated max rpm upon first commissioning, before accepting any warranty responsibility.
There's a big but, though.
Formalities and warranties aside, which obviously aren't relevant anymore on a 40+ years old boat, it can be desirable to overprop a bit a boat which quite likely is being used at hull speed most of the time.
Let's take Oscarvan's boat, which makes 19 kts wot, and let's say that she's really short of 150 rpm.
If he cruises at say 9 kts, as most folks do with boats like that, there is absolutely zero risk to overload the engines, at that speed/rpm.
If anything, by running at a slightly lower rpm and slightly higher load, he's doing the engines a favour, if you see what I mean.
But if he wants/needs to cruise as fast as the boat and engines allow, he'd better have the props shortened as much as necessary to reach the rated rpm at wot - no doubts about that.
I'm of the Pascal and Capt J school also to always be able to reach maximum RPM. I like that for many reasons including speed and performance, but also to be able to objectively evaluate the performance of the engines and know if everything is well or not. I hear your argument, Mapism, but don't agree with it. I don't think you're doing the engines a favor at 9 knots. I think the biggest favor you can do is to always have engines properly tuned and properly propped.
I don't disagree with your last statement, but many semi-displacement vessels are equipped with engines rated for 2300 rpm or more, designed for "normal" cruising operation anywhere between 1800 and 2000 (give or take, there are a few exceptions).
Now, it's not like they can't run at 1000 or 1200 for hours, of course. If that would be a big problem, how could SFs be used for fishing?
And of course, since SFs are not used just for trolling, but also for reaching the fishing grounds hammering the throttles like there's no tomorrow, I would never suggest to overprop boats with that sort of usage pattern.
But if a cruising boat whose powerplant is rated for 2300 is practically always spinning at half of that in real world, by running slightly (which is what I said, mind - not "hugely"!) longer props, the engines are possibly running at 40% load rather than 30%.
That can't be bad for them, can it?