Suitable inboard engines for a crackerbox

Discussion in 'Boat Design' started by EldonDav, Jul 26, 2015.

  1. EldonDav
    Joined: Jul 2015
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    EldonDav New Member

    Hey guys, new to the forum.

    I recently bought some plans from glen-L for a 15' crackerbox gentlemans style runabout. I need to really think about the inboard powerplant I want to drop in her before I start the overall design process. Looking for something that will be suited as more of a cruiser than a racer but also like it to have a little 'punch' when opening the throttle up. This is going to be my first build so anyone with good advice (especially from guys who have done similar builds in Australia) would be much appreciated.

    Cheers
     
  2. PAR
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    PAR Yacht Designer/Builder

    The Crackerbox is capable of taking just about anything from a little 4 cylinder to a small block Chevy (V8). It's very common to see the small block installed, because they're cheap, available and parts are available. Of course, this is way more power than this puppy needs, but this is also the whole point of the boat. Another issue with these type of designs is the shaft angle, which is severe to say the least. If you can get it below 15 degrees you're doing good, but you'll still need about 12 degrees, which isn't ideal. Lastly, because it's just a 15' boat, a transmission is difficult to fit, unless you go with a V drive (more weight, more expensive). The usual arrangement has no gear reduction, no reverse, no nothing, you start it up and she starts moving forward. I would recommend the Thunderbolt as an alternative, as it's long enough to use a V drive, with transmission, while still maintaining a reasonable shaft angle. It's still a straight shaft setup, which turn like crap, but you have the room to fit stuff without angling the engine up several degrees past optimum.
     
  3. FAST FRED
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    FAST FRED Senior Member

    One advantage of a nice oversized engine is you can usually install a vacuum gauge and cruise on the primaries , not the gas guzziling secondaries..

    At low (say 1500 or below ) rpm the noise is simply a bit above idle , a long term delight.
     
  4. PAR
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    PAR Yacht Designer/Builder

    The Crackerbox is basicly a racer, left over from the 50's and early 60's. They really suck at much less than blasting around on the edge of chine walk and/or proposing. These hull forms are not comfortable at all, pound unmercifully and will force you to personally know a dentist, so you can get knocked out fillings replaced. These boats are also well known for their ability, to bounce skipper and crew out, tripping and other assorted undesirable traits. They're the PWC of their day and fun for 15 minutes at a time, but pretty useless after this. The same concept in longer lengths can offer a lot more enjoyment, plus have enough room to carry a cooler of beer. The Cracker box is hard pressed to store a couple of PFD's.
     
  5. EldonDav
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    EldonDav New Member

    glen-l does does allow a 10% stretch of the whole frame. would this make the ride a little smoother or are there any modifications i can allow for a smoother ride. i have a toyota 1UZ-FE in an unroadworthy vehicle that i would like to marinize/marinise if possible.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The stretch will very slightly improve the ride, but it'll be a marginal thing at best. It's just the shape of the boat, which is early 1950's design philosophy. Take a look at any early 1950's car and compare it to what is common place today and it's the same deal. We've learned a bit in the nearly 3/4's of a century since it was drawn up.

    What do you want this boat to do? I'll bet there's a conversion available for this engine, but it wouldn't be my first choice. It's a good engine, but way more complicated than necessary in a boat like this. In most cases, simple is much better in a boat, so a quad valve, high strung, high compression engine (first gen UZ 10.5:1?), seems overkill on a boat that will perform quite well with a 200 HP 4 cylinder or a way under tuned V8 that isn't very highly stressed (read last a long time) and one that can use regular gas. Simply put, to me an OHV V8, with 8.5:1 compression and not working very hard to develop 220 HP, makes more sense.
     
  7. tom28571
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    tom28571 Senior Member

    Crackerbox as a cruiser? Do you drive to the office in a Bradley Fighting Vehicle? That is a similar concept. There are plenty of great runabouts that offer "punch" and Glen-L has some of them that would be way more fun than a crackerbox.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yeah, I don't know Tom, but I think this is what the OP needs to do - establish his priorities.
    I don't know what his idea of a gentlemen's runabout might be, but the Crackerbox isn't even close.
     

  9. rasorinc
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    rasorinc Senior Member

    Boy, old memories pop up. In 1958-59 I built the 12' flying Saucer in High School wood shop. Put in the water without decks and 4 people. My Dad 6'-5" 260 lbs. Two friends at 130 each and myself at 125 lbs for a total of 645 lbs. Hung a 35 hp Evinrude
    on it (borrowed)and roared out. Another boat ran along side and clocked us at 30 mph.
    Always wondered what a 60hp would do? 3 years ago I talked to Glen L Witt told him my story and he called me a Youngster................I was 70 then.....pardon my spelling. Put a 454 in that boat add 4' and go have fun------------wear a class 1 life jacket........................maybe 2.
     
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