I would think that in recent years, fuel economy and emissions are becoming buzzwords in the small boat motor department - forcing manufacturers to use 4-cycle gassers. Since its easier to make a 4-stroke quiet and they lend themselves well to sump-style lubrication (no gas-oil mix reqd) it makes sense.


I now have a new vacation destination - that place in Mass. that has PT boats on display - I thought battleship park in Mobile Bay AL was cool =)

-John

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2009 Kia Sedona
2009 Honda Odyssey EX-L
12006 Jetta Pumpe Duse
(insert Mercedes here)

Husband, Father, sometimes friend =)

That's the beauty of this place, it doesn't take long to find somebody who knows something.

I had an epiphany recently concerning diesels courtesy of Audi.

The last 10 years in diesel development equals about the previous 30 years. If that continues, what will the next 5 bring?

Good thread.

B

Another engine that isn't computer controlled - but a bit different in size!
Wonder what the HP to weight range is on these tiny gems? Didn't see a diesel, but they did have a Stirling!

http://nvbackflow.com/engines/

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John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E

About 2900 lbs each. PT boats had 3.

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MB-less

3? So it turned more quickly to port (or stbd) due to prop spin?

B

I have to get one of those!

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MB-less

Dunno. Counter rotating props on modern boats is relatively recent. You can get twin out boards that go opposite. I know on inboard engines with direct drive, you have to have counter rotating engines. You can get the crate marine motors from Ford (or GM) spinning either way. A gear reduction transmission makes it go the other way, so I suppose a tranny could make the prop spin the other way.

My guess is on a military boat you wanted everything to be identical for interchangeability. They might have had some sort of trim tabs to balance the torque, I have an inboard and the engine torque affects the level of the boat more than the steering. On mine the rudder is right behind the prop, if it is not behind the prop or if you have multiple rudders, it might not be a big deal.

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MB-less

Off topic a bit, but if you own a boat and buy gas at the marina, I can make you feel more sad: If pump gas is $2.75 for example, and marina gas is $3.5 for example, the marina is making .75 more for the gas, right? Nope. The pump gas has road use taxes built into the price, I think they are around .6/gal, depends on the state. Marinas don't charge that, so they are making .75 + .6.

In Texas if you use any pump gas off road, you can get a refund for the road tax by filling out a single form from the comtrollers office. Off road use is a boat, airplane, tractor, etc. FYI. Not a ton of cash but every bit helps and its easy to file.

On a similiar subject, if you remove the taxes from todays pump gas, and you go back to 1980 and remove the taxes, and you adjust the base price for inflation, we are paying less for gas now than we did in 1980.

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MB-less

I don't have much experience driving twin screw boats so I have to let that go. Single screw outboard boats (and airboats) have a decided difference in turning due to direction of prop rotation. Airboats I have driven turn faster to port. Not sure if that's the same for outboards.

Dang, I don't recall direction of prop rotation!

B

If my memory serves me, now remember I saw these PT boats 10 years ago. The center prop is a 4 blade, and is a RH wheel. But I was a little kid at the time so don't hold me to that.

2 stroke diesels have been gone in pleasure boats for the better part of 15 years, 4 strokes are king. They are being replaced by electronicaly controlled engines. The reasons are many, more power, faster spool up, lower fuel burn, emissions is starting to become a factor. MTU bought Detroit and killed them for the black box that controls the injection. Yanmar was the last hold out of mechanical 4 stroke diesels, but are coming over.

The power to weight of those Packards is good. 2900/1500=1.93 hp per pound.
http://www.yanmar.com.au/marine/cx_series/cxseries.htm

For example take a look at these 500hp I6 Yanmars, about as light as you can get 500hp diesels these days:
1815/500=3.63

All of a sudden those gas V12's look pretty good!

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2006 CL500
1969 280SE
2023 Ram 1500
2026 Genesis GV70
2007 Tiara 3200

I had a Mercury outboard that the prop turned to the right. I felt no steering torque because it had hydraulic steering. Outboard have 2 turns in the drive line so the effect is the same as direct drive in terms of direction, but you can get gear reduction though.

I have a ski supreme now (inboard), direct drive and it turns to the right (looking at it from the back). It turns easier (slightly) to the right. Worst thing about inboards (rudder boats) is the rudder does not work in reverse. The boat walks to the right big time. You can spin the boat by reverse and full left rudder going forward. Rock it like a car in snow, looks cool.

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MB-less

At least in CT if you buy over a certain amount you can get your road tax back. The reason fuel costs more on the water, at least up hear is several reasons:
1. You only get to use the gas docks from May 1 to early Oct here, before you run out of customers. Yet you pay for them year round.
2. Insurance is very costly, due to enviromental concerns.
3. Up keep is costly. Two weeks ago we replace our fuel lines going from the tanks to the fuel pumps. Total cost was $50,000. People don't see that.

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2006 CL500
1969 280SE
2023 Ram 1500
2026 Genesis GV70
2007 Tiara 3200

They consumed 158 gph at wide open throttle (each engine). The boats carried 3000 gallons of gas. thats 15000 lbs of fuel and it goes away fast!

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MB-less

The center prop would have a smaller moment than either of the other engines. Maybe the port and starboard props countered and the effect of the central screw rotation was small relative to the moments of the other two(?)

Is there an engineer in the house?

B

Don't get me wrong, I don't think marinas are supposed to give away money. Depending on where you are, your season will vary, and of course gas is not the only businessof a marina. Its just that if you focus on the gallon going in your tank, the marinas are making a much bigger profit (on that gallon) than the local station. But the cost of running that marina is higher as you said.

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MB-less