Vintage aluminum Crestliner project

Discussion in 'Boatbuilding' started by Alumination, Oct 24, 2013.

  1. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    That's an old, pre-63 series warped bottom hull (sea skiff style) and will become unstable around 40 knots.
     
  2. messabout
    Joined: Jan 2006
    Posts: 3,075
    Likes: 246, Points: 63, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    I do hope, for Aluminations sake, that he will heed these sage replies. He wants to make a silk purse of a sows ear. The nifty little Crestliner is not really a sows ear for its' purpose. It is a serviceable little boat with sansible limitations. It is a sows ear for his high aspirations. It is not suited for Aluminations purpose and any or all the modifications will lead to expensive, time consuming disappointment. He would be wise to build a proven boat that has been knowledgeably designed for speed and decent ride quality and therefore arrive at a happy ending.
     
  3. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I think if he just went down to the local marine and had a look see at how dramatically different high speed hulls are shaped, compared to his, he might realize how much work it would be. It can be done, but it'll sure look weird, in spite of the hard work.
     
  4. Alumination
    Joined: Oct 2013
    Posts: 84
    Likes: 2, Points: 0, Legacy Rep: -7
    Location: Knoxville, Tennessee

    Alumination Junior Member

    Yes. Any/all of the boat that will be in contact with the water once underway will be changed to a modern design that is better suited to more speed and better ride.

    I may have over stated my expectations. I'm certainly not looking for a 100mph boat that will run a buoy course. More in the say 60mph range that is easy to handle. A comfortable compromise between ride, speed and handling. Not a Fleetwood, Hayabusa or Elise.

    Many moons ago, in a Galaxy near Eustis, FL, Lake Jem to be more exact, a buddy of mine had a Hydrostream Vector/Viper/V-King, I don't remember which, the one with the "improved" pad which had a "hook" added to keep the bow down. Well, this "hook" on the platform/pad had very ill effects on handling and could cause the boat to fall off of the platform/pad and then make a quick turn which provided quite a bit of pucker experience. Another friend had a different model of Hydrostream, the one with the flat platform/pad and ran just beautiful. We basically just cut off, ground away the "hook" in the pad and made it look as much like the good running design as possible and it worked just as intended. Yes, I do realize these hulls were very similar in design to each other to begin with.

    I also helped a friend weld on a stepped platform/pad to a 14' aluminum jon boat. The bottom was typical square bow jon boat, dead flat with strakes and left the way it was except for where we added the material in the rear center. This was done to mimic the Hydrostream hull design and get the boat out of the water for increased speed and worked very well. Even seemed to handle better at speed and not turn as flat, it would roll a little more. We didn't consider the potentially catastrophic results.

    Yes, it will look strange on a trailer or hoisted in a boat dock, I'll live with that embarrassment. In the water I doubt much of the mods will be visible, even under way, maybe ride a bit higher in the water at speed.

    A few years ago I had considered building a wooden Barrel Back replica from Glen-L plans. Even then I was interested in changing the hull based on what I had read about how poorly the very flat bottom rode.
     
  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    You could see 40 on the hull as it currently exists. It'll be twitchy, but carefully handled, she'll get there. Even with a bottom change, asking a short, relatively fat hull to scoot to 60 will be testing longitudinal stability. You'll want a longer beam/length ratio at that speed, then what you have on that boat.

    To get a reasonably comfortable ride (at 60 it will not be), you'll want some V and preferably monohedren. I'd suggest no going insane with the deadrise, because it just requires more power for the same speed and this boat isn't likely to see a sea state where 22 degrees of deadrise will be necessary. 10 - 12 degrees will do, to soften the ride and permit smaller outboards, because you can only carry so much outboard on that boat, so optimizing for speed/weight is critical. This is one of the "dog chasing it's tail" issues you'll face. You want a softer ride at speed, which means more deadrise, but more deadrise means you need more power to get to that speed and the butt kicker is you can only support so much weight on the transom. It's not a reinforcement issue, but simply a weight on her butt issue. She can only hold up some much, because of the hull volume available. More deadrise will over a little displacement boost in this regard, but eventually, you'll run out of room.

    For example, lets assume you have a 1,500 load. This is boat, engine, fuel, controls, steering, battery, crew, supplies, cooler full of beer, etc.. Using a very generous 225 constant, you'll need a 100 HP to see about 60 MPH. This means you'll have to hang a 300 pound, 100 HP engine on a boat rated for only about 50 HP. Now if you hang a 300 pound outboard on the butt of that boat, what do you think is going to happen, even with a monohedren modest V bottom?

    What is the actual width of the boat at the widest point on the transom? Also what is the actual length, from bow to top of the transom? A simple formula can be used, to determine how much power you can place on her, which will govern your top speed a great deal.
     
  6. Alumination
    Joined: Oct 2013
    Posts: 84
    Likes: 2, Points: 0, Legacy Rep: -7
    Location: Knoxville, Tennessee

    Alumination Junior Member

    Widest part at transom is 4' 3" and length from top of transom to tip of the bow is 14' 1".

    Adding length is something I'd like to do to continue the lines of the boat into a barrel shaped stern. The lines are already shaped to go that way but have been stopped short.

    The dream was to have inboard power into either a surface drive or sterndrive. The sterndrive would be the easier and less expensive approach, no separate transmission needed, better maneuverability in reverse, possible to modify for more efficient surface drive like operation, etc. My desire for surface drive is not for shallow water operation rather less drag and more efficient propulsion.

    I do love the sound of a V-8 but I happen to have a Suzuki SV1000 engine, 996cc, water cooled, 6-speed, V-twin, ~120hp / 80ftlbs at the crank.
     
  7. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Okay, that boat is a fair bit smaller than I thought and using the usual formula for figuring how much power you can toss at her, she's only rated for a max of 40 HP, You could probably bump to 50 with no ill affects, other then the very low transom cutout height, which would tend to ship water at times. A typical 50 HP outboard will be in the 200 pound range, which is a lot for a little butted boat to hold up without swamping every time you back off the throttle. Theoretically, you could make a taller transom, for a long shaft outboard and solve part of this issue, but there's still the weight thing. Simply put, you only have so much volume to work with to hold up any motor/drive combination.

    You might as well all but forget about anything other then an outboard on a boat of this scale. An I/O is out of the question, just because of weight, an inboard, leaves you with few places to sit, which will likely be very hot too, a V8, even a 385 pound Buick or Land Rover, plus it's trans/drive is just way too much, though admittedly, the only cool sound you could have aboard.

    The solution is more boat, both in length and to some extent, beam too. You need immersed volume, both for planing and to support a considerable more powerful engine/drive package.

    This means you'll have to cut the boat down the centerline, make it wider, then stick a whole new bottom on her, possibly longer. There's not much left of this little tinny, once you do this, begging the question why not just build something more suitable.

    There are lots of barrel backs to choose from, some having been upgraded to modern under bellies, so they can go faster and are more comfortable at speed (a relative term). I don't know of any that are aluminum, but a conversion could be performed by any reasonable designer or NA, for not much money. In fact, this is a very common request we perform yearly for clients.

    In the end, I think you'll find marrying the bottom of a go fast hull to the top of your tinny, quite difficult, because they're very differently shaped. For example if you look straight down on your boat, you'll notice it has a lot of volume forward, compared to a bass boat, which has most of it's volume well aft of this. A bass boat will have a pointy triangle shape, while yours is more truncated teardrop like. This is just because of when they were designed and how they approached getting to boat on plane (two different approaches). The bass boat planes on her aft most sections and carries 3/4's of the forward part clear, while your boat planes on it's midship and aft sections, just holding 1/4 to 1/2 the boats length clear at speed. This is why your boat has more volume forward than a bass or flats boat.

    Make a couple of small balsa models of each boat, one like yours and one like a go fast bass boat, then cut the two along the chine of LWL and see how they match up. You don't have to be real precise, as the shape differences will be come apparent quickly enough so show what you need to see, in regard to your proposal.
     
  8. Alumination
    Joined: Oct 2013
    Posts: 84
    Likes: 2, Points: 0, Legacy Rep: -7
    Location: Knoxville, Tennessee

    Alumination Junior Member

    Where might I find barrel back designs with updated underbellies?

    Why start with this boat? She has the shape I'm trying to achieve above the waterline.

    Typically a stern drive needs no transmission between it and an engine, correct?
     
  9. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Your little boat can't hold up a stern drive and an engine. The smallest stern drive is in the 120 HP range, which is way over what your boat can handle.

    [​IMG]
    [​IMG]

    A little longer than your boat, but just thought to tease a bit. Notice the engine size on these 18' tinnys.

    The barrel back feature can be added to any boat with enough effort. A 60 MPH, 14' boat is another thing all together. I used to race a 60 MPH boat about that length, but it was nearly dead flat bottom (the fast way to go for top speed), wasn't remotely comfortable at any speed over 30 MPH, regardless of the cushions used and it was really dangerous to to turn at speeds over 35 MPH. Lots of friends have been hurt in these puppies and a buddy of mine was killed last spring racing one, but yeah, you can do it.

    Find a 60 MPH hull you like, buy the plans and make the barrel back modification yourself or have it done by a designer.
     
  10. Alumination
    Joined: Oct 2013
    Posts: 84
    Likes: 2, Points: 0, Legacy Rep: -7
    Location: Knoxville, Tennessee

    Alumination Junior Member

    Is there a length to width ratio one uses to keep a boat stable at speed? Minimum length? Longer the better?

    Maybe someday I'll start from scratch and build a completely new boat from plans. For now I intend to modify this "tinny".
     
  11. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    There are preferred ratios, but no set rules or guidelines. Essentially, you have targets to need to hit and adjust dimensions (several) to make things hit where you'd like.
     
  12. Alumination
    Joined: Oct 2013
    Posts: 84
    Likes: 2, Points: 0, Legacy Rep: -7
    Location: Knoxville, Tennessee

    Alumination Junior Member

    Where would one find these ratios and the several dimensions?
     
  13. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    These aren't things you can look up, but are determined by many, often conflicting factor during the design process.
     
  14. thill
    Joined: Mar 2007
    Posts: 82
    Likes: 2, Points: 0, Legacy Rep: 26
    Location: Virginia, USA

    thill Junior Member

    I know this reply is a little late, but I am in the process of restoring/rebuilding an old 14' aluminum boat that had been gutted by the previous owner, and used as an open crabbing boat.

    When I bought the boat, I mainly bought it for the motor. No title, no BIN, no idea of who made the boat. And to be honest, I didn't care much, as the hull shape wasn't very pleasing to the eye from the side view. It looked slow and clunky, and maybe tippy, due to the very rounded back section and chine. (what I now know is referred to as a barrel back)

    But when I got her in the water, the ride was AMAZING. Surprisingly fast, and super-soft riding, through small chop and larger waves. Like NOTHING I've ever experienced in an aluminum boat!

    This made me VERY curious, as this boat has a round back and a very large spray/lifting rail angling from high on the bow to low in the stern. But I could find nothing. I finally discovered a little stamped piece of metal that said "Crestliner" on it, so I went to their forum, and got my answer!

    Turns out, I have a 1957 Crestliner 14' Viking 710. Here is the original catalog page from when it was new:

    [​IMG]


    What surprised me is that these boats came from the factory with a 60 HP Evinrude (or a 40) and were used to waterski. Good and stable up to about 45 MPH.

    Alumination, from a quick search, the boat you probably have is the Commodore 14:


    [​IMG]

    It is rated for 35 HP, which will get you to a very respectable 30 MPH+. That feels GREAT when you are in a boat this small, and the ride of these boats is exceptional.

    But I would venture to say you will not "safely" turn this into a 60 MPH boat, no matter what you do to it. BUT, if you can find an older bass boat with a soft floor, (OFTEN on Craigslist for FREE) and put your time and resources into that, it WILL reach the potential you are seeking safely.

    I currently have an old Glasstream HydraBass that is tickling 60 with a Mercury 90 HP on the back. FUN!

    Either way, best wishes, and stay safe!

    -TH
     

  15. Alumination
    Joined: Oct 2013
    Posts: 84
    Likes: 2, Points: 0, Legacy Rep: -7
    Location: Knoxville, Tennessee

    Alumination Junior Member

    Yes, I think you are correct about the model being a Commodore. The rounded chine at the stern is not referred to as a "Barrel Back". Barrel Back refers to the shape of the stern above the waterline.

    [​IMG]

    I have been behind small aluminum and fiberglass boats on water skis, Hydro-Slide, wake boards, tubes etc. It sure wasn't as nice and easy as say a Ski Nautique and possibly considered reckless endangerment by today's standards but this is what we had, funds permitting.

    I haven't started any mods yet, mostly got the boat for the vintage shape of the hull above the waterline. I have researched tunnel hull design quite a bit and will probably go that route, seems to be a superior design in almost every aspect. I'm sure it won't qualify as "Safe" but that is how I roll, on the edge. :D
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.