To repower or not part 2

Discussion in 'Wooden Boat Building and Restoration' started by rattleandbang, Aug 5, 2015.

  1. rattleandbang
    Joined: Apr 2015
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    rattleandbang Junior Member

    Howdy Gents. I have a 28' cruiser built by the venerable Jensen's boat yard on San Juan Island in 1957. Very similar in style and design to a Chris Craft Constellation of the Period. It's powered by a single Crusader 220 (307 Chev) that's been rebuilt at least once in it's life. Displacement hull. The vessel is in excellent shape as tens of thousands in restoration funds were dropped into her in 2006.

    We were sailors for many years and this is our first powerboat. We don't mind quiet and slow, so we generally run her close to idle, which in calm conditions can give us 4.5 knots, and running with the tide over 7 knots at times. Operating her like this we generally burn about 4 litres an hour, which is tolerable (our last sloop, a 36-footer, usually burned 150 litres for an entire season, used almost constantly). But when the chop gets up or we have to fight a current, the fuel consumption increases at a staggering rate. A recent trip in rough conditions and contrary tides, burned 90 litres of fuel to do 11 miles, doing 5-6 knots. That was a bad day.

    I'm considering repowering her with a 50hp westerbeke diesel I currently own. My rationale is I want to be able to open her up a bit when fighting wind or current without opening a vortex in the tank. Our sloop weighed just shy of 16,000 lbs and was powered by a 30 hp diesel that was adequate in most conditions. I figure this Jensen Cruiser displaces less than half that. The Crusader will push her to 16 knots but the fuel economy is beyond ridiculous, never mind the noise and vibration, so 99% of its capacity is never used. I'm happy keeping this boat to hull speed or less.

    Does anyone have any ideas of how much that will effect fuel consumption? Is it worth the cost of retrofitting everything? Like I said, I'm happy to mooch along with the current engine, but even a small movement beyond idle, say 1200 RPM, and she triples her operating costs. Running against a 2 knot tide requires that kind of expense. I'd prefer an engine with a greater potential power range without such a range in operating costs. I want to go far, not fast. Is there a way to roughly calculate speed/engine RPM /fuel consumption with a diesel engine like this?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    You used 90 litres to go 11 miles ? When are you going to fix the hole in the fuel tank ? :D I am at a loss to understand how you can use 4 litres per hour @ 4.5 knots (admittedly on smooth water) but it escalates to 45 litres an hour at 5-6 knots in rougher conditions, by a rough calculation.
     
  3. missinginaction
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    missinginaction Senior Member

    It seems to me that you're talking about two different types of boat. Sailboats are very efficient and slip through the water cleanly, powerboats not so much generally.
    While 90 liters of fuel seems excessive, you are trying to push a lot of boat into a strong wind and current, this takes power which means fuel. That said it does seem that your fuel consumption is excessive. I'm especially suspicious of your comment that any increase in RPM off idle increases fuel consumption dramatically in any conditions.
    Before I'd consider a re-power I'd take a look at your engine, especially the fuel delivery, ignition and timing. Based on your comment you were out for a little less than 2 hours and burned 90 liters. This would work out to at least 3/4 liter PER MINUTE (120 minutes running time X 3/4 liter = 90 liters total burn), or almost one US ounce of fuel every two seconds.
    Your carburetor might be a good place to start. Does a spark plug check indicate an over rich condition? Engine running at proper temperature? Engine tuned to spec? Compression good? How about alignment?
    All these things play a part.
     
  4. rattleandbang
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    rattleandbang Junior Member

    To be honest, these responses give me some hope, as I had always heard that power vessels suck enormous fuel and so I simply assumed that this was normal. But the volumes of fuel used are real; in fact, my First trip in the vessel (we just bought it) was broken into two legs, more or less equidistant: Port Townsend to the south end of Lopez Island and from Lopez Island to Oak Bay, BC. The first leg was in rough conditions and at least partially against a 2-knot current, and I sucked a full tank dry just off Lopez. 90 litres. That was a shock as I had only been going at about 1400 RPM. I was then worried that I wouldn't have enough fuel to make it the rest of the trip, so I decided to make sure I went with the current and kept the throttle below 1000 RPM, and once I arrived in Oak Bay, I couldn't see that the fuel level had actually changed in the second tank. No gauges; fuel is measured with the old stick in the tank.

    Since then, we've had other occasions where the same is repeated, like this past weekend, where 30 min of 1400 RPM burned much more fuel than 4 hours of 900-1000 RPM. So this isn't typical for a vessel of this size?

    To be honest, I haven't had the time yet to go over the engine, but it starts immediately and runs smooth and powerfully. I've checked to make sure she isn't dripping into the carb bores while underway.
     
  5. gonzo
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    gonzo Senior Member

    Do you have a four barrel carburetor? It may be that the secondaries are either out of adjustment or the jets are the wrong size.
     
  6. rattleandbang
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    rattleandbang Junior Member

    It's a Rochester 4GC 4 barrel, but trust me, the secondaries never open. It's designed so they only open once the primaries are wide open, which has only happened once when I checked to see what her top speed would be. With no mufflers and that kind of fuel suck, she never sees that degree of throttle.
     
  7. gonzo
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    gonzo Senior Member

    You can expect 10HP/hr per gallon of gas on a well tuned engine. That means that the 220 HP engine in your boat should burn about 22 gallons ( 82.5 liters) per hour at its maximum power output. Something is wrong with the fuel system to burn so much gas.
     
  8. DCockey
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    DCockey Senior Member

    How is your stick calibrated? Have you verified fuel consumption by amount of fuel to refill tank?
     
  9. missinginaction
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    missinginaction Senior Member

    I'll wager this is a carburetor issue. It's been quite some time since I played around with q-jets. We used them on drag cars some 35 years ago. What you have there is "pre quadrajet".

    The link below might give you a little more back round on your 4gc, especially the beginning of the article.

    http://www.hemmings.com/hmn/stories/2007/01/01/hmn_feature29.html

    Should your engine be in good shape and you decide to replace your carburetor you might consider a Holly Marine Carb. I use a 450CFM Holley specific to my 302 Ford V8 in a boat only slightly smaller than yours. Fuel consumption is reasonable.

    https://www.holley.com/products/fue..._carburetors/marine_carburetors/parts/0-80551
     
  10. rattleandbang
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    rattleandbang Junior Member

    Thanks all. I've actually got a service manual for this carb. I've already had it apart to clean out loads of crap from the float bowls. Rebuild kit waiting for me at the jobbers when I get home. Then we'll see. I'm tempted to swap the thing with a new replacement, but I put a new $500 Holly on my 73 motorhome, and had constant problems with sticking float needles since new. Of course Holly blames it on "modern gas". Given that experience, If possible I'd like to reuse the original.

    What should I expect fuel economy with a boat like this?

    The stick is simply marked out 12" from the bottom, which is the depth of the tank. From there I simply note how far the level appears up on the stick. You get a rough idea of the level. Probably accurate to 1/8 of a tank increments by eyeball.
     
  11. gonzo
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    gonzo Senior Member

    Q-Jets have better idle characteristics and are more economic at low speeds because of the small primaries. They have a huge amount of adjustment combinations, and won't work right unless you get the correct combination. Check the jet sizes, rod weight, spring color (gives the stiffness value), float height. Another common problem is the acceleration pump. If the check ball valve is missing or stuck, it will pour gas into the throat as you rev up.
     
  12. sdowney717
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    sdowney717 Senior Member

    I used to have 4GC carbs, went with Quadrajets and used an adapter from spreadbore to squarebore, made myself from epoxy coated plywood.

    The 4GC's I had when the boat rocked, they would cut the motors in and out, and that rubber boot leaked fuel, bilges always smelled of fumes. when motors turned off the heat would make that worse, and the carbs heat soaked fierce, took 30 minutes to restart hot motors as they would percolate and flood.

    The quadrajets dont do any of that. They have smaller primaries but whether that helps fuel economy in a boat, I doubt it. the idle circuit can suck a lot of fuel on a carb. But you cant go too lean or it may miss and a miss means it is wasting fuel. I am wondering if advancing the timing to favor slow rpm versus high rpm would improve fuel economy. Like installing a vacuum advance on distributor. At WOT, the vacuum advance would go to zero, but at less throtte position, vacuum advance will advance the timing. Boats were setup for WOT, so maybe they dont bother with vacuum advance? But might it help for part throttle operations?

    Think the USCG if they saw a vaccum advance on a distributor would have an issue with that?
    My Palmer marine engines using IH392 from 1970, have Holley distributors with a Vacuum advance bolted on, but not connected, and this is OEM.

    Squarebore and spreadbore intake is available for the chevy 307.
    http://www.summitracing.com/parts/s...gxXQOniVyndqn_f8uDDc3lsaM_guaLnwMURoCm77w_wcB

    So any carb can be used. A heat spacer phenolic or wood is a good idea between the intake and the carb.
     
  13. gonzo
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    gonzo Senior Member

    Vacuum advance is only useful in cars because the loads vary a lot. Also, once a car accelerates and uses high power, the engine runs at relatively high RPMs with little load. Boat are different. The load increases with speed and remains high.
     
  14. sdowney717
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    sdowney717 Senior Member

    My thinking though is low load running only at idle or just a little higher, maybe having greater advance then would use less fuel. For higher rpm use say above 1500, no extra timing advance than the mechanical advance built in to distributor.

    This would be fairly easy to test. Simply advance distributor 5 degrees and test fuel consumption at a low RPM say 1000 rpm compared to the OEM static timing. On my boat OEM is 10* BTDC, so advance to 15* and see if the fuel used is less, the same, or more than at 10* BTDC.
     

  15. rattleandbang
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    rattleandbang Junior Member

    All very good suggestions, especially tuning for low vs high speed. Fortunately I don't have any of the problems listed with this 4GC carb, except for the inevitable evaporation of gas from the fuel bowls once the engine is shut down, which floods the bilge with fumes. I find it very strange that the air intakes on these inboards aren't ducted to the outside; the float bowls are not small and there's a good cupful or more of gas that evaporates into the boat as it sits hot.

    I've been researching the circuits on this thing and I notice that the power piston opens a fuel valve in the bottom of the float bowl. It's vacuum actuated but if it hangs up at all it could keep that valve open allowing excess fuel into the bowl. Lots of things could cause a running rich problem, though. The question is whether to take this cruddy thing in and have them boil it clean and rebuild it or buy a rebuilt. Right now the accelerator pump doesn't work because the outlet is corroded closed. I've cleaned an incredible amount of crap out of this thing. This is what I sucked out of the float bowls:

    [​IMG]
     
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