Repower? How committed are you to life at 7 knots?

[Nomad Willy]

Fletcher500,
OK good. This is pleasure boating and we should run what we like.

boathealer,
Very good considering the GH is a very beamy boat and wide boats are at a disadvantage re efficiency. What's you're cruise rpm and rated rpm?

 

[boathealer]

boathealer,
Very good considering the GH is a very beamy boat and wide boats are at a disadvantage re efficiency. What's you're cruise rpm and rated rpm?

Cruise 1800-2200. 2850 WOT. Beamy is good to live on

 

[Nomad Willy]

Would that be JH 55hp Yanmars? Are they the ones rater at 3000rpm or are they the earlier versions rated at 3800rpm?

I wonder how they did that? As far as I know both engines are rated at the same power and nothing else seems different. Impossible I suspect. I suspect they just took a stroke w the pen and that was that.
Looks like the engineers designed the best engine they could but after a time marketing said buyers are buying other engines rated 800rpm lower. So they “fixed” it.
Whadda think?

 

[LarryM]

Would that be JH 55hp Yanmars? Are they the ones rater at 3000rpm or are they the earlier versions rated at 3800rpm?

I wonder how they did that? As far as I know both engines are rated at the same power and nothing else seems different. Impossible I suspect. I suspect they just took a stroke w the pen and that was that.
Looks like the engineers designed the best engine they could but after a time marketing said buyers are buying other engines rated 800rpm lower. So they “fixed” it.
Whadda think?

Eric,

On the later 4JH5E, Yanmar increased the bore from 84mm to 88mm and kept the same 90mm stroke. The displacement increased from 2.0L to 2.2L. RPM dropped from 3,800 to 3,000 and horsepower from 56 to 54. I've been told they are a lot easier to live with.

 

[AusCan]

This brings up not only the question of what speed you may want, but the question of how much reserve power do you personally need?

For example, personally I never had need for much. The thousands of miles of ocean travel was always at one speed. Heavy tidal currents... waited them out. But I didn't live in Bay of Fundy, Anchorage or other challenging areas like some here. My boat was powered at 6hp per long ton. If I repowered I would install half that (and will on my new build).

Regarding to "crossing open water in unfavorable" weather. When the seas build past 12ft, hitting 20ft or more, are you really going to want tons of reserve power to battle against the angry Gods? No way. You'll power back to 4 knots and focus on surviving.

Mr. HeadtoTexas raises very practical comments and questions here, not theoretical.

For me 7 knots is pretty much flat out and I'm usually happy doing 5 to 6 knots. The strongest currents around here are less than 4 knots, so I'm always making headway.
I've yet to wish that I had a bigger engine.

btw - everyone seems focused on the fact that it may not be a wise economic decision to repower with a smaller engine. Surprise! surprise!
Owning a pleasure boat is never a wise economic decision. Why should re-powering a boat be any different. Just do it if that is what you want.

 

[Mako]

btw - everyone seems focused on the fact that it may not be a wise economic decision to repower with a smaller engine. Surprise! surprise! Owning a pleasure boat is never a wise economic decision. Why should re-powering a boat be any different. Just do it if that is what you want.

Yeah, no kidding brother! I sold my boat after a few years for (theoretically) a 30% profit. However when I deposited the cash in the bank up sale, I had lost about 100k. Damn, where did all that money go???

 

[boathealer]

Would that be JH 55hp Yanmars? Are they the ones rater at 3000rpm or are they the earlier versions rated at 3800rpm?

I wonder how they did that? As far as I know both engines are rated at the same power and nothing else seems different. Impossible I suspect. I suspect they just took a stroke w the pen and that was that.
Looks like the engineers designed the best engine they could but after a time marketing said buyers are buying other engines rated 800rpm lower. So they “fixed” it.
Whadda think?

4JH4E - 3000rpm. Never heard of a 3800 version...

r

 

[LarryM]

4JH4E - 3000rpm. Never heard of a 3800 version...

r

Yep, 4JH3E is rated 56hp @ 3,800rpm. The continuous rating is 50hp @ 3,650rpm. Fine engines, but they do sound busy. I ran one for a number of years in my former trawler Boomarang and it was absolutely trouble-free. The current owner has put many more miles under her keel and last I heard, the only failure was a tachometer.

 

[boathealer]

Yep, 4JH3E is rated 56hp @ 3,800rpm. The continuous rating is 50hp @ 3,650rpm. Fine engines, but the do sound busy. I ran one for a number of years in my former trawler Boomarang and it was absolutely trouble-free. The current owner has put many more miles under her keel and last I heard, the only failure was a tachometer.

Yep. Agree on the Yanni. 4481hrs (as of 9:00am today) on each of the pair of slower 4JH4's, and both are purring (albeit loudly) like kittens....

 

[Nomad Willy]

Ahhh yes Larry,
“On the later 4JH5E, Yanmar increased the bore from 84mm to 88mm and kept the same 90mm stroke. The displacement increased from 2.0L to 2.2L. RPM dropped from 3,800 to 3,000 and horsepower from 56 to 54. I've been told they are a lot easier to live with.”

I’ve heard nothing but good about both engines. And somebody told me they didn’t change the obvious ... but they did. I thought about a JH for Willy but .. too much power. But my favorite 54hp engine is an Isuzu. Passed on that for the same reason. Had an HM Yanmar and it was fine but too much aluminum and a bit noisy.
Thanks again all

 

[HeadedToTexas]

Excellent conversation. Should the opportunity to own a sound boat in need of repowering present itself when the buying window opens in several years, I'll reopen the debate then. For now, making enough power to cruise at 7-8 knots can be done efficiently by darn near any engine and certainly by the one the manufacturer chose during design. Makes perfect sense. Thanks to all.

 

[billhall]

I do not believe repowering is cost effective unles the current moter is at lifes end Even if it is. while you may not use the power much, It will come in handy on those days you are bucking a head wind and or seas. The exter power will be a belssing and you will not max out a lower power unit.

 

[daviddraper]

Why semi-displacement?

I have a 2006 MS 34 Trawler with a single Yanmar 370. I cruise at 2000rpm which gives me ~7.6kts.
I run much faster if conditions or time constraints require. If I was going to repower to get ONLY hull speed, I would want a full displacement boat. Semi-displacement Mainships (well at least mine) are horrendous in a following sea. The flat aft sections, short keel and smallish rudder makes it very difficult downwind and a little extra power, which puts more steering pressure on the rudder helps.
I was crossing Tampa Bay literally yesterday in 30+kt winds and 6’ waves. As it was I was having trouble with broaching, slower and less power would have been worse. Buy your 390, run at hull speed and rest comfortably knowing you have a speed reserve.

 

[silentfaith]

The original poster seem to say he has not looked at many trawlers and likes the mt 390, nothing wrong with that boat but there are some butes out there that do 7 knots and he should look around.

 

[Nomad Willy]

daviddraper wrote;
"If I was going to repower to get ONLY hull speed, I would want a full displacement boat."

You won't cruise at hull speed w a FD boat. A knot or so less. Many FD boats can't make hull speed even at WOT. For hull speed cruising you'll need a SD boat.

 

[long-cours.62]

When we bought this ex patrol boat we had the project to fit smaller engine because as you can see on the speed/consumption tab for the hull speed we don't need an hudge amount of power.And at "low speed" don't need so much power...but finally we sold her and she was used as a ...tug boat to tow a ...700t boat during 1200 nm at 3.5kts (yes some people are more crazy than me )

But the main problem at so low speed with this type of boat it is the roll !

Trawleurisation d'une ex vedette rapide !? - Trawler long-cours


With our LC62 at 7 kts (the targeted speed of the initial question) we do 4.67 nmpg for 33t and 18.26m wl and 4.35 beam at wl


For the actual may the solution will be derated the engine it is a pair of C12 actually rated at the "maximum" 710 hp, but is saw they could be rated at (for example) 350hp with some little change.
But after asked to Cat France they said the most expansive change ..it is get "electronic program" from Cat !?