hull designs on a 17' powerboat

Discussion in 'Boat Design' started by curtis73, Mar 13, 2002.

  1. curtis73
    Joined: Mar 2002
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    Location: Variable, North America

    curtis73 Junior Member

    Hello to all. I'm a new guy. I'm an avid fisherman and have lots of boating experience (I'm surprised my parents didn't name me Evinrude), but I'm about to embark on my first boat building experience.

    I have a few quandries. I'm really entranced by the Glen-L Thunderbolt. For those of you who don't know, its a shallow vee speed boat, just over 17', wood ply plank design. It says of the Thunderbolt's design: "Hull type: Vee bottom with flaring sides that act as anti-trip chines" Here's a link:

    http://www.databoat.com/Page_ProductDetail.asp?sid=148&pid=3389

    On Databoat's site there is also a boat design called the Rampage. Here is a quote from the description of the Rampage: "The lift strakes on the bottom of the Rampage are just like the ones proven on the hot competition ocean racing boats which make all the headlines. They give you a flat, dry ride with easy steering, besides letting you get out of the hole like buckshot out of the barrel."

    Here's me: "great...what's a lift strake? What's an anti-trip chine?" I've seen newer 'glass performance boats with stepped hulls that provide lift kinda like a hydro sponson on the bottom.

    What I'm wondering is, what are the elements of a hull and how do these elements affect speed, handling, and ride in the choppy water? I know the obvious factors, like a 12 degree vee hull will be faster than a 20 degree, but not take chop in dry smooth composure. The lake I fish on the most is a typical wilderness lake which sees its share of chop (up to about 3'), but I don't go out on those days anyway. I've been known to fish and ski in 1.5-2' chop, but after that, the wind is so strong it makes casting too hard and trolling too hard to keep lines untangled. Not to mention, its hard to sunbathe on the deck when you're constantly getting tossed off. ;)

    My current boat is a 1958 Montgomery Ward Sea King 14' aluminum with a 25 horse merc. My other boat is a 1968 Glassmaster 15' tri-hull. Both are for all intents and purposes a flat bottom boat. I'm used to getting beaten up and wet when the wind blows.

    If you look at the pictures of the Thunderbolt, it looks like anything more than a 6" chop would take water in over the back. One thing that will help me is that I won't be using a big block, I'll most likely be using an all-aluminum inline 6 that will be half the weight. Power will be in the 250-270 hp range with torque from idle to redline. Gotta love L-6s.

    Now that I've given you some background on me and my boating... The Rampage clearly has the favorable design for ski/recreation for my uses. Unfortunately I think the rampage is just about as ugly as they come. Would it be possible to incorporate some of the Rampage's better ride/dryness/handling characteristics into the hull of the Thunderbolt? I would be happy to give up 10 mph to get a little more versatility. I don't want to fundamentally change the plans or change cuts of wood, just maybe with some epoxy, plywood, and 'glass add on some lift steps of something. Any help on hull design explanations would be appreciated so I can maybe see what needs to be done and what can be done.

    Thanks so much.
    Curtis

    PS. Any other designers I should consider?
     
  2. Jeff
    Joined: Jun 2001
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    Location: Great Lakes

    Jeff Moderator

    Hi Curtis,

    Welcome to our forums!

    Have you already found the Glen-L web site for more photos of these three designs?

    [​IMG]

    Tornado

    [​IMG]

    Rampage

    [​IMG]

    Thunderbolt

    Keep in mind that I believe all three of these designs (and descriptions) were created a couple decades ago so what was phrased as revolutionary features on raceboats then has become commonplace now. Note that I don't have anything at all against the Glen-L designs - in fact I like many of their designs. They are well proven, and it's nice to build a design which was good then and is good now, and it's also fun to see a part of the past be brought to life today and be new again. I suppose in a way it makes time less linear as designs which sparkeled as cutting edge in one era are introduced to a new generation...

    Whey they say "The lift strakes on the bottom of the Rampage are just like the ones proven on the hot competition ocean racing boats" I'm pretty sure (though I could be mistaken as I don't have any hands on experience with either one of these designs) they are simply referring to standard fore-aft running strakes like the ones found on practically every production v-hull boat built today, triangular sections which lay against the angled plane of the hull to create 2-4" flat surfaces, breaking up the hull to reduce the wetted area subject to spray and deflecting water to add lift. I believe since you are adding flat surfaces, the more strakes you add, the harder the ride will be, but of course this would only apply if the number/size was excessive compared to the size of the hull.

    As to "anti-trip chine" I believe they are referring to the flared section of the side/bottom which prevents this area from catching, especially in a sharp turn. At least Glen-L refers several times to the flared hull sides aft, and I don't see anything which deviates from what I think of as the standard, but maybe someone will point out a detail I'm missing here.
     
  3. Guest

    Guest Guest

    Only if you stop or let a wave overtake you :D

    I've never personally liked a boat with that open and low of a stern, but I think it could take a little more than that - say at least 18 inches if they were really breaking and much more if they were rolling. As long as you were under power you would be fine though. I've seen a few boats built like that, very low in the back, with a metal or clear splash guard to protect the engine from being hit by the boat's own wake which looked a little silly.
     
  4. curtis73
    Joined: Mar 2002
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    Location: Variable, North America

    curtis73 Junior Member

    wow, thanks

    Wow, great info, guys. Thanks.

    Jeff, I see what you're saying about the strakes. Little water-grabber-linear-keel things. Makes sense. That sounds like something that could either be added or compensated for. I can picture even a 1 inch alumunim center strake to keep it from turning like a flat-bottom. As far as 20-year old hull designs, I also understand. My youngest boat is 35 years old. Are there other designers with similar "retro" topsides like the Glen-L who have better or newer hull designs?

    I agree with "guest," Don't let a wave overtake you! I think the low, flat stern is exactly what makes me choose this Thunderbolt design over the elliptical tail of the Rampage and others. It just looks mean :)

    I'm going over to another forum and post some questions about powerplants.
     
  5. Jzastrow
    Joined: Feb 2002
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    Location: Elgin, IL

    Jzastrow New Member

  6. Nomad
    Joined: Feb 2002
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    Location: Florida

    Nomad Senior Member

    curtis73 Aren't these guy great!:cool:
    Here is a summary the lifting strakes do just as they are named they help lift the boat out of the water faster. The down side is that they also cause drag thus needing more Hp. Where as a boat with a flatter bottom can with the right design and less power have the same top end and with less power is better fuel economy. The downside acceleration is slower, handling is not as good, as well as rough water performance.
     

  7. Nomad
    Joined: Feb 2002
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    Location: Florida

    Nomad Senior Member

    :mad: Just one mistake in regards to the boats with out strakes handling it is with the right design some of the best boats in a head and 1/4ing sea. The weakness is in following seas.:cool:
     
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