heavy displacement repower dilemma

[Salmoneyes]

Originally Posted by PeterS

The 4 cylinder B does vibrate more, 4 cyl engine 2 pulses per revolution, 180 degree cycle, 6 cyl 3 pulses per revolution, 120 degree cycle.

A V8 is very slightly less smooth than a 6 cyl, basically from there the more cylinders the smoother the engine. The straight 6 also delivers the most torque for its size.

I had a feeling it would get explained.. Thank you...

Im getting some advice that I would be better off to have 6cyl at that 100hp range than a 4cyl if my only concern was weight, and the savings was under 500lbs.

It was explained to me that torque was more important in a heavy boat when maneuvering, especially around other boats.

[PeterS]

As it has been the holidays, boredom set in and I found myself monitoring the Forum, it never ceases to amaze me how many fights develop so I tiptoe around carefully and really only decided to respond to a couple of threads where the OP's were not getting answers to their questions. You might notice that since mid 2007 I have only posted once until today!!

I am sure your NA has given you the torque advice, and he or whoever is absolutely correct.
Any heavy displacement boat will require torque rather than HP and on top of that a lot of ratio in the transmission, in your case I would look at around 150 HP and a ratio of 2.5:1.

Also diesel engines do run on x number of grams of fuel per HP/Hour, in the old days (last Century) that figure was around 140 to 160 grams, recently I have seen that figure fined down to around 120 to 140 grams. I say this just to confirm that an earlier comment you made was in fact correct, with a Diesel the amount of HP you use is based on the HP required to do the job you command which determines the fuel consumption, it really is as basic as that.

you could of course put 2000 HP in your boat, but you would find that it would be trying to climb onto plane at idle (Now we wait for everyone to jump in and .......).

HP by the way is a nothing measure it is calculated from torque and that primarily happened back in the 1800's as a way of categorizing power, whereas torque is a figure that describes actual work done.

Not sure what your shaft diameter and material is (was it 43mm?) but if you like I can tell you what HP your current shafting will handle if I know diam & material and RPM (your Mercedes RPM & HP would at least set a start point as it seems fairly typical).

No worries if you don't, but I am not looking to sell you anything, just interested in helping.
Not sure where you are based but I get the impression it may be west of me.

Let me know and we can e-mail.

Have a happy new year

[Salmoneyes]

Originally Posted by PeterS

As it has been the holidays, boredom set in and I found myself monitoring the Forum, it never ceases to amaze me how many fights develop so I tiptoe around carefully and really only decided to respond to a couple of threads where the OP's were not getting answers to their questions. You might notice that since mid 2007 I have only posted once until today!!

I am sure your NA has given you the torque advice, and he or whoever is absolutely correct.
Any heavy displacement boat will require torque rather than HP and on top of that a lot of ratio in the transmission, in your case I would look at around 150 HP and a ratio of 2.5:1.

Also diesel engines do run on x number of grams of fuel per HP/Hour, in the old days (last Century) that figure was around 140 to 160 grams, recently I have seen that figure fined down to around 120 to 140 grams. I say this just to confirm that an earlier comment you made was in fact correct, with a Diesel the amount of HP you use is based on the HP required to do the job you command which determines the fuel consumption, it really is as basic as that.

you could of course put 2000 HP in your boat, but you would find that it would be trying to climb onto plane at idle (Now we wait for everyone to jump in and .......).

HP by the way is a nothing measure it is calculated from torque and that primarily happened back in the 1800's as a way of categorizing power, whereas torque is a figure that describes actual work done.

Not sure what your shaft diameter and material is (was it 43mm?) but if you like I can tell you what HP your current shafting will handle if I know diam & material and RPM (your Mercedes RPM & HP would at least set a start point as it seems fairly typical).

No worries if you don't, but I am not looking to sell you anything, just interested in helping.
Not sure where you are based but I get the impression it may be west of me.

Let me know and we can e-mail.

Have a happy new year

That was great response, (hard not like when it coincides with my thoughts)..

Always appreciate help, and this forum provides a ton for me. I know a little about a lot of things, but certainly don't know a lot about any thing.

The shaft is 45mm, and the whole unit is a Rodahlaxlar oil bath stern tube assembly from Sweden. We are looking seriously at the Evolution Marine Shaft System to replace it with. Not sure at the moment about the shaft material.

Says FL on your tag,,, I worked for the Forest Service in Bradenton at the Myakka District HQ.

[PeterS]

what is your e-mail?
I dont go on facebook or twitter stuff!!
need confidential chat with you

[PeterS]

sorry that sounded goofy!!
Just dont want a lot of OZ guys harassing me!

[PeterS]

The following link may give you some alternative ideas, PM me if you want more info

Fleming Yachts

[mako]

Originally Posted by LotNick

What about one of those Chinese clones? Simple, naturally aspirated, HF-4102 at 70HP should be less than 4k USD with gearbox included. I would definately investigate...

Probably the best Chinese marine diesels are the Weichai. Very solid. There's a (natural gas engine) research and sales division in Chicago, plus others in Europe and Asia.

[mako]

Originally Posted by nhschneider

I would never consider installing a Detroit Diesel - it has one of the worst weight-to-horsepower ratios of any engine out there.

That's exactly what you want in a heavy displacement vessel - the bigger the engine and the lower stressed it is, the better. The OP wants to reduce weight, but I doubt he wants to go with a tiny, 3000rpm Yanmar.

Salmoneyes - if you get your vessel down to 30,000 lbs then you would be well served with a 2-71 or a 3-71. You should consider if you prefer to power at close to hull speed (as opposed to crossing oceans) most of the time. Also since you are a motorsailer then you have all the windage to contend with.

Originally Posted by nhschneider

They’re noisy, inefficient, they tend to leak badly (called ‘seepage’ by the manufacturer as leaks are covered by warranty),

True, although mine only leaked a little bit

Originally Posted by nhschneider

they vibrate terribly

in what universe? a 6 cylinder 2-stroke is one of the smoothest engines around. Perhaps what you are referring to is the incredibly intense sound making everything around it vibrate (like my teeth)?

Originally Posted by nhschneider

and parts are expensive.

that must be a typo. You meant to say "least expensive parts, outside of China"

Originally Posted by nhschneider

Yes, they’re reliable but most modern engines are.

I hope by modern engines you are not referring to common rail, computer-chip controlled engines

[Delfin]

Originally Posted by Salmoneyes

Yep, very popular here in Oregon... Keel cool is to allow the engine to run at proper temps (190 to 200) but we will run wet exhaust.

With keel cooling marinization is unimportant, even with wet exhaust since sea water injection is all downstream from the engine. Isuzu makes some wonderful engines that are used for irrigation in Asia, requiring continuous operation for months at a time.

[Salmoneyes]

Originally Posted by Delfin

With keel cooling marinization is unimportant, even with wet exhaust since sea water injection is all downstream from the engine. Isuzu makes some wonderful engines that are used for irrigation in Asia, requiring continuous operation for months at a time.

Are those made by Isuzu? Read some place Isuzu was branding Kubota made diesels? I could have that wrong though....

[Delfin]

Originally Posted by Salmoneyes

Are those made by Isuzu? Read some place Isuzu was branding Kubota made diesels? I could have that wrong though....

AFAIK they make their own. They made over 2 million of the C series, that I had, and that is now replaced with the J series.

[Simi 60]

For those that claim diesel engines need to be run hard, reality says something different.

To me, the easiest way to gage whether slow speed running is detrimental over years and years of operation is to look at commercial fishing vessels with older designed engines from Detroit, Cat, Cummins, etc… Revisiting the “Detroit” mystique again, its longevity was built on engines rated to run at 1900-2100 RPM and above, but could only last for 30+ yrs when operated continuously at 1100-1600 RPM (again, well under 50% of rated HP)..These same engines in a “crew” boat used in the off-shore oil industry, would go through “top-ends” (or worse) just about yearly when run at close to their governor settings..The longest-lived engines that I’ve been involved with (hrs and yrs wise), have been engines in commercial or recreational trawler type applications run at 50% of rated HP or less..Yes, there are many other parts of the equation that leads to the life of a diesel engine, but I know from experience that running them slow (i.e. cruising for days on end at hull speeds or less) is NOT a cause for concern. But some obvious things to watch out for (when running slow) are being sure your coolant temp stays up to spec. and watching for any signs of wet stacking or slobbering..Some Detroits seem to do this, but I think it’s more of the general condition of that particular engine and is sometimes related to the design of the exhaust system.. A few minutes a day at higher cruise HP levels should be all that is necessary to clean things up should it be needed..

In closing, I’ll mention that although this topic is brought up quite often and many people preach that you’ve got to use a diesel hard if you want it to last, I’m still waiting to find one that was rebuilt before its time due to low speed use..Just the opposite seems to be always the norm

https://www.sbmar.com/articles/low-s...arine-diesels/

[Delfin]

Originally Posted by Simi 60

For those that claim diesel engines need to be run hard, reality says something different.

++

[boatpoker]

Originally Posted by shakey doug

Perkins HT 6354. [Horizontal]

I had one of these and put 20,000hrs on it before I rebuilt it. Wish I'd never sold that boat.

I don't understand the OP's claim of 7gph. that seems excessive. My HT6-354 burned only 1.6gph at 7.5kts and the 37' boat weighed 30,000lbs.

[hpeer]

You asked for input from folks out there. We live aboard about 6 months/year and are now in Carribean. 44’ steel cutter, 40,000 pounds, Yanmar 4JH4-TE, 72hp, 1-1/4” long shaft, 3 blade prop. 2,200 hours.

At 2,000 hours I had the engine serviced by a Yanmar shop and they found a turbo bearing going bad, shipping from Japan took a few weeks. Not excessive cost. I get a wee bit of oil into the turbo from the breather line.

Shaft starts to vibrate above 2,200 rpm so I usually run below, which is ok cause I’m close to hull speed by then and cheap anyway. I frequently motor sail to wind for hours at 1,500 rpm. I’ve had no carbon build up in the exhaust elbow. I do run her up once in a while to burn out the turbo.

We are 1/4” keel and 3/16” above. I’m no NA but if I heard you right your extra plate weight is all in the hull topsides. That will make her a bit too heavy, but increase resistance to roll, mass at a distance from roll axis. I like the 6mm hull. But you want to move weight DOWN in the boat as much as OFF the boat.

I forget your water tankage but consider a water maker for weight savings. We have 180 gallons of water with no water maker. We’ve yet to have a problem. But I’ve been told we are stingy on water usage. A water maker adds complexity in the mechanics but then you don’t have to worry about getting crap water, which we just did. Drinkable but a lot of silt.

Not to overstate the obvious, in your situation I would prefer to eliminate a pound high over a pound low. Yet we tend to add arches and solar that are really high. I would try to keep my batteries high, out of flood water reach, which is counter productive.

One thing I’ve seen done that might be helpful is to move the chain locker closer to amid ships and down on the ballast. Gets the weight out of the bow and puts it down low in the hull near center of rotation.

Good luck, big project. Which design?

2. HEIGHT of motor. The Mercedes is 32 inch tall. A lower motor will allow lowering floor in pilot house, allowing to lower pilot house roof, which makes windows smaller all adding benefits to the overall project requirements.

This is a great observation, moves weight down but also reduces your hulls sail area making her easier to handle in a marina in a cross wind.