Luxury on a miser budget - Page 3

dimer2 · 12-02-2013, 05:33 PM

At about half the speed of that Sabre lol. 1400 rpm is comfortable at 9 kts

Art · 12-02-2013, 09:09 PM

One engine - Two props - Gears to run em - Drag created - Loss of goods if grounding happens, props, shafts, struts, rudders - - > OMG - - > I concur with Don i.e. Moonstruck post 34!

And I therefore feel it is good for me to repeat my post 18.......

Good Golly Molly!! - IMVHO!!

Unless you simply like to spend money and/or work REAL hard for hundreds of hours: Just locate a real good condition pleasure trawler/cruiser and do what these play-boat craft were meant to be for - i.e. "Pleasure Boating, Cruising, Hooking, Gunkholing, Swimming, Relaxing, Partying... etc!"

Darylat8750 · 12-02-2013, 09:37 PM

I love this concept.

I want to point out that Al (the OP) mentioned 6.5 to 7.5 knots. With the waterline length of the boats that we are considering on this thread that is a very economical speed and a requirement for very little horsepower at cruise. My OA 44 with 2 Ford Lehman 120s will cruise at 7kts using 2.55 GPH. This indicates less than 45 hp is being used (assuming about 15 hp per gallon per hour). Cruise at 8.2 kts doubles that fuel burn. I feel that my boat would be very satisfactory with engines 60hp or maybe even less. My friend built a boat out a a burned out Hatterras 53. He added a bulbus bow and extended the stern into a wet deck. His boat will cruise at 8kts on 4 GPH.

So my question is: How little power do you think would still be satisfactory to push a 38-45 foot boat in a displacement mode assuming we would never expect it to plane. Just go 7knots even against a lot of wind and head seas. The smaller the less expensive. The more efficient. The issue then becomes, how little is too little. Has anyone operated a boat when they thought it was underpowered purely in the displacement mode?

FF · 12-03-2013, 06:22 AM

>Has anyone operated a boat when they thought it was underpowered purely in the displacement mode?<

To be underpowered in displacement mode would require the boat to be out in seas that few choose to see.

A 50K breeze does not require the HP of climbing 12-15 ft waves at speed.

In most big wave cases the fact that the boat goes slower is not the hassle.

IF an engine were sized to operate with 80% rated hp and 90% rated speed . thats as good as it gets for most HD diesels.

Would not be the RPM /power choice for car transplants , which should be loaded like gas engines.

rjtrane · 12-03-2013, 09:25 AM

We built the original Great Harbour 37s with a pair of Yanmar 39 HP diesels. During initial sea trials, we recorded top speeds of 8 knots plus.

The move to 54 HP motors was primarily a marketing move - to most shoppers, the 39s seemed too small. Of course, they weren't too small - just perceived as too small.

The larger motors do have the benefit of extra power for fighting headwinds and better single engine performance. Disadvantage, as perceived by some, was the larger motors had turbos while the smaller ones did not (IMO, turbos are a good thing if they are engaged/providing boost at cruising RPMs).

In other words, I agree with those who say that very modest HP motors are all that is required for cruising a boat efficiently - around 1 knot below theoretical hull speed (6-7 knots or so). It makes sense to choose a size that will get you to hull speed; any more becomes reserve power for against the wind and/or single engine performance.

ranger58sb · 12-03-2013, 04:25 PM

Quote:

Originally Posted by Al

On the market there are currently many larger size boats that are powered with twin 454 gas or similar. These boats are on the market quite reasonably priced for the value within. I use as an example the following example:
Tollycraft Sedan Bridge 37

Here we have a 34 foot boat with twin engines at a very good price. Under the concept being discussed would be the re-powering of the boat with twin inexpensive diesels

Likewise, if one reads the Christ Craft forum, one finds the perfect platform in even larger boats that beg for such a conversion concept.

for this discussion offered are three current Ebay advertisements for same model/make engines.

...

Combine the price/shipping/tear out/re-place cost with two of the above engines plus the price of the boat seemingly would present an opportunity to obtain the stately finishings of a modern large boat at a very attractive investment amount.

Was traveling, not sure I fully reviewed the whole thread, but at risk of repeating what maybe others have said...

If you find a gas boat you like, you can enjoy it at slow speed with the existing engines for LOTS less than it would cost to convert to diesel.

Just use it, as is. When the original gas engines crap out, replace with reman gas engines (or new, or rebuild, whatever) and keep using them at slow speeds.

Fuel savings on smaller diesels often seems to be a useful goal, but if you do the math, I suspect it almost always works out better to just keep what ya got. Otherwise, you spend $50K on a gas boat (for example), another $25-75K to convert it (including tanks and genset and so forth)... and you end up with a boat with $51K -- with a fuel burn rate maybe half or a third what it would have been with the gassers.

(Dock neighbors converted their sportfish from gas to diesel, after having blown one of the originals. I'm told they spent approx $100K on the conversion, including genset. Shortly thereafter, they listed it for sale at $125K, and it apparently hasn't sold yet.)

So compare the fuel cost of a 1000 mile journey at 8 GPH vs. 3 GPH, for example... and how many trips like that you need to offset your $25-75K (whatever) conversion cost.

That said, HULL FORM should also be part of your equation. Typical twin engine gas boats with planing hulls simply aren't comfortable all the time in all sea states. Beam seas especially suck. OTOH, with twin gas planing hull, you also have a option of stepping up speed a bit to become more comfortable. Or tack. Or delay movement until weather becomes friendlier. Or pick a different destination. And so forth.

Seems like it would be an interesting project... but I would guess the math usually makes it more economical to just go slow. Many of those bargains are out there because the CURRENT owner isn't willing to go slow, but if you are, your gain.

-Chris

Darylat8750 · 12-03-2013, 05:33 PM

" Typical twin engine gas boats with planing hulls simply aren't comfortable all the time in all sea states. Beam seas especially suck."

I have a full displacement hull and beam seas still suck.

Really wish I could afford stabilizers......

FF · 12-04-2013, 06:14 AM

with a fuel burn rate maybe half or a third what it would have been with the gassers.

The diesel sellers may promote this myth but reality is gas is nowhere like double the fuel burn per hp.

An outboard , old 2 stroke is not too efficient but 10 hp per gal is common.

Old auto engines are as bad 10gp/gal as they are usually run on small boats at 3000 -4500 RPM , up on their power curve.

At modest speeds , where the secondaries do not open 12 hp gal is not hard.
Tho here too a smaller engine size helps with economy.

Todays complex electronic fuel injected cars get a nice 14 hp per gal, even tho the programing is for the air police , not especially for fuel economy .

Most older diesels are in the 16 HP / gal area,,,, BUT ONLY if they are of the proper size to carry a good load. Most HD diesels need 50-60% of rated HP to get there.

With a turbo and operated in the best range , some can see 20 HP/gal .

The really modern complex fuel injection diesels (4 squirts per firing) can see 22-24 HP / gal , at least on the builders dyno.

So for most its a gas car engine at 10-12 hp gal, vs an old diesel that needs great sizing and prop choice to see 15-16/HP/gal.

200% difference NO ,,,300% difference no.,,,,,,25% difference , perhaps.

That is why commercials (thousands of hours a year) always run diesels .

For most pleasure boats the lower diesel fuel burn is easily eaten by the difference in maint and parts .

IF Da Book is followed.

Diesels with car oil, car antifreez and no winterizing or out of service requirements met , can be cheaper ,,, for a while.

rjtrane · 12-04-2013, 08:49 AM

I don't recall seeing any mention of slow speed handling of a planing motor yacht. It is my experience that many fast boats don't track well at slow speeds requiring a lot of steering.

One consideration, therefore , is to drive the prospective yacht at the intended speeds; 7-8 knots. Some have better longitudinal stability than others.

Mentioned before is heavy weather sea keeping - seems to me the motor yachts under consideration never were meant to be ocean voyaging, all-weather cruisers. Regardless of power and speed , they are designed for good weather.

Darylat8750 · 12-04-2013, 11:14 AM

"Mentioned before is heavy weather sea keeping - seems to me the motor yachts under consideration never were meant to be ocean voyaging, all-weather cruisers. Regardless of power and speed , they are designed for good weather. __"

+1 here! A sport fisherman or anything with a lot of glass doesn't make sense for real long distance off shore voyaging. Of course my old body isn't really suited for serious extended heavy weather anymore either.

Coastal cruising and carefully planned Caribbean island hopping should be well within the prudent capabilities of the boats we are thinking of.

" It is my experience that many fast boats don't track well at slow speeds requiring a lot of steering. "

I wonder how much expense would be involved in adding some keel area to a sport fisherman to help with low speed tracking. The best way would be if that could be done while incorporating prop protection with the same structure.

There was a 46' Hatteras sport fisherman in Isla Mujeres a couple of years ago with bad DDs in it. Basic boat was in pretty good shape and it could have been had for a song...... Drove me nuts but I walked away.....

ranger58sb · 12-05-2013, 06:24 PM

I have not found slow speed tracking to be much of an issue, given "displacement-friendly" sea states. When sea states aren't friendly, roll has been the more noticeable factor.

And the AP usually doesn't have any significant problems with the boat at slow speed, as long as we're running on both engines. Sometimes wind can overpower the autopilot (when we're trolling at 2.5 kts) but that's not too much of a deal. Running on only one engine with the rudder over adds some AP strain, I think; wind is more easily able to hose up the track in those conditions. Remembering I can't reef my flying bridge.

Yes, that was my point about supposed diesel fuel savings over gas: at whatever savings rate, it takes a boatload of savings to cover the cost of conversion... and I'd suspect the math won't usually support it.

-Chris

Darylat8750 · 12-05-2013, 09:55 PM

The auto pilot does fine on my friends stretched Hatt. 53. I do fine in day light. At night with no stars and quartering waves I have to work harder than I want to or need to do with my boat to hold a good heading.

kulas44 · 12-07-2013, 08:27 PM

Just subscribed, mostly because this subject interests me very much. Especially changing out gassers to diesel, chevys in particular, 454's even more so. First a clarification, SAE bellhousing patterns do not apply to gasoline engines used in boats. Older gassers are mostly counter rotating, so that needs to be taken into consideration. The absolute easiest swap is the old 6.5 or 6.2 chevy diesel (at about 150 hp non turbo ) in place of a 454. Everything bolts up, motor mounts, bellhousing, cooling system, trans, etc. It really is a straight swap. Been there done it. Any decent DIYer can do it. The 6.2/6.5 is a great and very economical engine at less than 200 hp. It will run a day less than forever at low loads, and they can be had on the cheap. At 310 hp they are grenades with a loose pin. Kinda like a Lehman in that respect. That being said, my current project is a 48 foot sportfisher with a pair of 8v92s at 550 hp each. I really hate these engines, for no particular reason other than I dont need them for the way I use the boat. At low loads, maybe 8 knots, for extended lengths of time, combustion temps get really low and she really starts loading up. Kick it up for awhile and it cleans out, good for a few more hours. The problem is that at low power levels Detroit Diesel cylinders and pistons are basically air cooled. They move a lot of air. It also has 9215 injectors that are pretty big, but not huge compared to 735 hp models that use 9240's. As much as I dislike these engines, I love the boat. So,,,,my plan is to remove them and replace with a pair of dodge cummins 6bt's, now rated at 215 hp, but will be 195 when installed. I will have the pumps rebuilt and rated at those specs. Thinking of maybe installing them non turbo'd, rated more like 120 hp. Boat is 46 foot lwl, 16 foot beam, 50,000 lbs. 34 inch wheels. Need about 120 hp to get to hull speed, w.a.g. but close. So I dont "need" 400 hp. But propped correctly the rating doesnt make a difference anyway. Turbo or not kinda dose, but as long as the engines will turn 2500 rpm thats not a big deal either. It has 2 to 1 gears in it now turning 32 x 34 props, 3 bladed. A 3 to 1 gear with the 6b's should be in the ball park with these props, and making about 9.5 knots. Anyway, I can do the work, and enjoy doing it, resale does not concern me, probably be worth more with the 6b's anyhow. Your thoughts are appreciated.

BerettaRacer · 12-08-2013, 04:37 AM

Quote:

Originally Posted by kulas44

Just subscribed, mostly because this subject interests me very much..........That being said, my current project is a 48 foot sportfisher with a pair of 8v92s at 550 hp each. I really hate these engines, for no particular reason other than I dont need them for the way I use the boat. At low loads, maybe 8 knots, for extended lengths of time, combustion temps get really low and she really starts loading up. Kick it up for awhile and it cleans out, good for a few more hours. The problem is that at low power levels Detroit Diesel cylinders and pistons are basically air cooled. They move a lot of air. It also has 9215 injectors that are pretty big, but not huge compared to 735 hp models that use 9240's. As much as I dislike these engines, I love the boat. So,,,,my plan is to remove them and replace with a pair of dodge cummins 6bt's, now rated at 215 hp, but will be 195 when installed. I will have the pumps rebuilt and rated at those specs. Thinking of maybe installing them non turbo'd, rated more like 120 hp. Boat is 46 foot lwl, 16 foot beam, 50,000 lbs. 34 inch wheels. Need about 120 hp to get to hull speed, w.a.g. but close. So I dont "need" 400 hp. But propped correctly the rating doesnt make a difference anyway. Turbo or not kinda dose, but as long as the engines will turn 2500 rpm thats not a big deal either. It has 2 to 1 gears in it now turning 32 x 34 props, 3 bladed. A 3 to 1 gear with the 6b's should be in the ball park with these props, and making about 9.5 knots. Anyway, I can do the work, and enjoy doing it, resale does not concern me, probably be worth more with the 6b's anyhow. Your thoughts are appreciated.

This is almost identical to the project I have in mind. The 50' hulls I'm looking at mostly come with the 6v92's (535-550hp), a few were upgraded (back in the day) with the 8v92's. Well nowadays those engines are pretty much worn out, short lifespan fuel guzzelers. Was also considering the Cummins 6BT's (in 200-250hp)as an alternative. On the boat I'm running now, I have the Cummins 6BT's (at 160hp) as generators (1800rpm), they've been a reliable engine. A few years ago at 12,000 hrs each we did a top end just to freshen them up, and I've since put 1500 hrs each since. Thats 27,000 hrs with no real concern. Fuel burn as a gen averages 3GPH. Thats probably about the same power I'd need to push a hull 10-12 knts, (Intracoastal cruising speed). That would give me 1.5-2 MPG, with plenty of HP in reserve to get out of the shit in case of weather/current etc.
A side benifit is the weight savings, the 6v's are about 3500lbs, the 6BT's about 1200. I can add a large house battery bank upgrade and a tender, and still be less than original boat weight.
Right now still in the thought/planning stage.

FF · 12-08-2013, 05:43 AM

Right now still in the thought/planning stage.

The physical part, removing 3500 lbs of iron is frequently the biggest challenge.

Regardless of what some yard butchers say,,chopping a hole on the side of a steel or aluminum boat is fine , but not in GRP.

A patch is possible but no real repair .

kulas44 · 12-08-2013, 07:42 AM

On my boat, a 1988 ChrisCraft Commander 482, engine removal/replacement is easy. Except for the size and weight factor. The rear salon door and window are removable and a portion of the wall comes out, leaving a space big enough to get the engines out by reaching in with a boom crane or extending fork lift. The salon floor comes out. P.O. had a yard remove the original engines in preparation for a repower. That went south when he did the math and I bought the boat for the yard bill basically, 12k. We fixed up the engines and put them back in. The inside exhaust manifolds need to removed but are easily reinstalled once in the boat. The biggest problem I have is the weight loss (not from all the work I'll be doing, from the boat) of about 5000lbs. The boat is already a little stern light, enough so that with empty water tanks I have a problem with cockpit deck drainage. It carries 500 gallons of fresh water and 8 t105 batteries and 250 gallons of fuel, plus a 15 kw gen under the cockpit sole. With everything full, including the other 700 gallons of fuel in 2 centerline tanks in the engine room, it sits level. I will need to add some weight somewhere aft. So far I have not needed more battery capacity, but more would be ok. I have a pair of ME2000 inverter/chargers that provide ac power when not running the gen. and battery charging. Doubleing the bank size will still only add about 800 lbs, not nearly enough. The boat will not be used for offshore passage making, just near shore stuff. I am thinking of adding removable internal ballast under the genset. Lead bars encased in concrete and bolted into the stringers would be doable. External heavy plating is possible, thru bolted to the hull. Adding a lead keel ???. Your thoughts are appreciated.

BerettaRacer · 12-08-2013, 07:53 AM

Engine removal/replace is pretty much the same with the hull I'm looking at, remove cockpit seating, lift the hatches, and boom the engines out. They're V-drives, so rear/tranny mounts will set location, fab some new front mounts, get a vendor in to build new exhaust.

Forkliftt · 12-08-2013, 08:23 AM

Quote:

Originally Posted by kulas44

Just subscribed, mostly because this subject interests me very much. Especially changing out gassers to diesel, chevys in particular, 454's even more so. First a clarification, SAE bellhousing patterns do not apply to gasoline engines used in boats. Older gassers are mostly counter rotating, so that needs to be taken into consideration. The absolute easiest swap is the old 6.5 or 6.2 chevy diesel (at about 150 hp non turbo ) in place of a 454. Everything bolts up, motor mounts, bellhousing, cooling system, trans, etc. It really is a straight swap. Been there done it. Any decent DIYer can do it. The 6.2/6.5 is a great and very economical engine at less than 200 hp. It will run a day less than forever at low loads, and they can be had on the cheap. At 310 hp they are grenades with a loose pin. Kinda like a Lehman in that respect. That being said, my current project is a 48 foot sportfisher with a pair of 8v92s at 550 hp each. I really hate these engines, for no particular reason other than I dont need them for the way I use the boat. At low loads, maybe 8 knots, for extended lengths of time, combustion temps get really low and she really starts loading up. Kick it up for awhile and it cleans out, good for a few more hours. The problem is that at low power levels Detroit Diesel cylinders and pistons are basically air cooled. They move a lot of air. It also has 9215 injectors that are pretty big, but not huge compared to 735 hp models that use 9240's. As much as I dislike these engines, I love the boat. So,,,,my plan is to remove them and replace with a pair of dodge cummins 6bt's, now rated at 215 hp, but will be 195 when installed. I will have the pumps rebuilt and rated at those specs. Thinking of maybe installing them non turbo'd, rated more like 120 hp. Boat is 46 foot lwl, 16 foot beam, 50,000 lbs. 34 inch wheels. Need about 120 hp to get to hull speed, w.a.g. but close. So I dont "need" 400 hp. But propped correctly the rating doesnt make a difference anyway. Turbo or not kinda dose, but as long as the engines will turn 2500 rpm thats not a big deal either. It has 2 to 1 gears in it now turning 32 x 34 props, 3 bladed. A 3 to 1 gear with the 6b's should be in the ball park with these props, and making about 9.5 knots. Anyway, I can do the work, and enjoy doing it, resale does not concern me, probably be worth more with the 6b's anyhow. Your thoughts are appreciated.

Great post. VERY informative!

kulas44 · 12-08-2013, 08:24 AM

What gears. Mine has the Allison MH20's. Not really compatible with the 6bt's as far as I can tell. If they were I could just change to a 3-1 ratio.

ranger58sb · 12-08-2013, 08:39 AM

Quote:

Originally Posted by kulas44

The absolute easiest swap is the old 6.5 or 6.2 chevy diesel (at about 150 hp non turbo ) in place of a 454. Everything bolts up, motor mounts, bellhousing, cooling system, trans, etc. It really is a straight swap. Been there done it. Any decent DIYer can do it. The 6.2/6.5 is a great and very economical engine at less than 200 hp. It will run a day less than forever at low loads, and they can be had on the cheap. At 310 hp they are grenades with a loose pin. Kinda like a Lehman in that respect.

Seems to be a decent option for OP's consideration. About what would it cost? (Perhaps assuming OP doesn't do the heavy lifting.) Would existing fuel tanks/lines work? Exhaust components?

And then there's the genset...

Seems to me the most useful comparison would be cost of gas over time with original (and replacement gas, when necessary) engines... versus savings in fuel over time after a conversion (and with converstion cost amortized into the latter).

Or something like that

-Chris