Engine Power N37

Home Forums Other Boat Systems Engine Power N37

This topic contains 7 replies, has 4 voices, and was last updated by  James Wascko 1 week, 4 days ago.

  • Author
    Posts
  • #8663

    James Wascko
    Participant

    Greetings,
    Ok before I begin I want to state this thread is NOT about gaining speed and I thoroughly understand the FD hull and maximum speed.

    37 = 54hp and 47 = 75hp

    Let’s say it came time to rebuild.
    If one repowered with 75hp in a 37.
    1. Would you be able to maintain cruising speed of 6-8 knts. With less power or throttle?

    2. Allowing reserve power (more power) to use in heavy current and or strong head winds …..
    To enable keeping knts up higher rather then dropping down or making no head way?

    Have seen some heavy current on the st. Lawrence and have seen some boats almost not make it through with their single screw.

    PART TWO
    Does Having twin 54 hp engines make a huge difference over a single screw of same hp in the same situation?

    Been thinking about this for awhile now so I am asking you veterans for real insight.

    Thank You
    Jim

  • #8664

    Chuck Truthan
    Participant

    Jim,

    I’ll be the first to put my foot in my mouth.
    Just the other day, I dropped one engine to neutral and watched what happened. I lost about 1 knot of speed and had to turn a little bit of the wheel to compensate for the asymmetric thrust.

    The other big difference over a single screw, is when one engine drops off line, you can still keep going. Then there is the two engine maneuvering capabilities that a single engine does not enjoy – because bow and stern thrusters also break down.

    As to increasing the horsepower, you’d probably have to change the props as well to take advantage of the extra power. But I’m guessing at that. There are others that know far more than I. From 54 to 75 HP is a 39% increase. Theoretically you want to obtain a 39% increase in speed, which would be from 6.0 kts to 8.4 kts. I also don’t know if you’d have to change out the prop shaft for a larger diameter one, which would also require a new cutlass bearings and perhaps a larger diameter shaft pipe (proper term escapes me) going through the hull to the cutlass bearing. You will also have an increase in fuel burn, which means reduced range on 500 gallons unless you change one of the water tanks to a fuel tank. Then you have less water aboard, unless you have a water maker aboard. All that depends upon the type of cruising you want to be doing.

    One thing I did talk to Lou Codega about to improve performance, and that is to make smooth the bottom of the swim platform. He said that would improve performance IF THE SWIM PLATFORM ATTACHMENTS WERE STRONG ENOUGH TO TAKE THE EXTRA LIFT FORCE (a question only Ken can answer which I’ve not gotten around to asking yet.). At full fuel and water in our N37, I’ve noticed a porpoise pitching in calm waters. there is also water coming over the top of the swim platform. This has to be decreasing the efficiency of the vessel. I’m guessing a 4 to 5% decrease in speed (0.2 to 0.3 kts).

  • #8665

    Joe Pica
    Participant

    The swim platform mod was done by Tom Cooper on his N-47. Last I spoke to him he said that he does not have any real data for a delta. I have not experienced any porpoising on my N-37 flybridge with it’s heavily loaded bosun locker and lazarette (however the swim platform does have water washing over it. I have been in a lot of seastate and current and don’t feel the extra HP would make that much difference. If you only go up to the turbo’s version you may be able to use the same shaft, prop etc. the clearance of the prop to hull, sand shoe and rudder is a critical dimension. So any change in those relationships will necessitate a cascade of cost and major refits. Both Mike Borum on a N-47 and Fred Mangelsdorf on an N-37 went up the lower Mississippi River against the current at times only making 2 knots SOG. Note Hull speed formula is speed through the water not over the ground. against a current you must add the opposing current speed when approaching that theoretical limit. That limit doesn’t move much with hp. with our displacement only hulls.

  • #8667

    If one repowered with 75hp in a 37.
    1. Would you be able to maintain cruising speed of 6-8 knts. With less power or throttle?

    [Dick] – HP required to move the hull at any given speed does not change, so the same power is required regardless of the power source. The 75 hp engines would create that amount of hp at lower rpm’s than the 54 hp engines, so yes, the throttle position would be “less” but fuel burned would be virtually identical.

    2. Allowing reserve power (more power) to use in heavy current and or strong head winds …..

    [Dick] – I don’t think so. Again, the governing factor is the FD hull and the power required to move it through the water.

    To enable keeping knts up higher rather then dropping down or making no head way?

    [Dick] – I don’t think so. At wide open throttle, my 54 hp engines drive Avocet at hull speed (8.1 kts). I’m pretty sure that the availability of more power would generate more hp, increase fuel burn and push Avocet higher on her own bow wave, but it would not change her speed through the water.

    PART TWO
    Does Having twin 54 hp engines make a huge difference over a single screw of same hp in the same situation?

    [Dick] – Absolutely! Widely spaced as they are, our twin engines are “poster children” for proportional throttle operation. When coupled with rudder positioning, you can even crab the boat sideways. I’m pretty sure that isn’t possible with a single screw vessel. My personal favorite advantage of having twins is redundancy in the event one side is disabled (e.g., overheating, mechanical problem, bad fuel, prop damage). Well worth the higher preventive maintenance costs, in my humble opinion.

    [Dick] – PS, you can add transmissions to Chuck’s list of running gear that would be potentially be affected by re-powering an N37 with N47 gear. If you really wanted to do this, it might be cheaper to buy an N47, and then remove ten feet from the hull and shorten the shaft. Fun to imagine what that would be like!

  • #8671

    Chuck Truthan
    Participant

    Hey if you do by a N47 and cut off 10 feet, I’ll take the 10 feet!

  • #8673

    How about we split it 50/50, Chuck? Where would you put your five feet? I would extend the cockpit, keeping a foot or two for the saloon.

    Dick Hermann
    N37 Avocet

  • #8675

    Chuck Truthan
    Participant

    Since the 10ft comes out (or in) forward of the pilot house, I’d ad 1 ft to stateroom 2, 6″ to head and the rest to the master stateroom so I can bend over without getting a door knob up my …

  • #8678

    James Wascko
    Participant

    Thank You Every One,
    I do understand about what you can do with twins and I will not purchase a single engine trawler.

    I was kind of referring to the difference between say a single 54 compared to a twin 54’s in the same current head on.

    Will running the twins tend to take on more then the trawler running a single?

    I have run outboard for the most part.
    I know if I ran twin 150 4 strokes I would run right with the guy with a single 300 4 stroke give or take a mile or two an hour.

    Trying to learn if the twin 54’s would not be affected as much as the single in the same current.

    10 feet? For me that’s easy
    10 more feet of Tender hauling Space.

    Thank you again
    Jim

    • This reply was modified 1 week, 4 days ago by  James Wascko. Reason: Spelling

You must be logged in to reply to this topic.