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Thread: Sport C tunnel boat

  1. #1
    ExperiMental BYOBoat's Avatar
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    Default Sport C tunnel boat

    Last year I built a sport c tunnel boat. It runs ok, but needs some major changes. Currently the sponson bottoms are way too long. I also have some weight balance to do. Weight aft it porpoises, weight forward the XL running surfaces stick to the water and acceleration out of the corners takes forever. Plan is to get the running surface length fixed so I can move the CG forward enough to get out of the porpoise, but still get corner acceleration. Here's the boat now, hopefully adjusted before the weather changes.
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    mini tunnel boats for sport, now an experimental Sport C added to the fleet.

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    Here's the boat mid last year before the initial series of bottom adjustments

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    mini tunnel boats for sport, now an experimental Sport C added to the fleet.
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    ExperiMental BYOBoat's Avatar
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    Got the bottom cut out and new panels fit. Won't be the best structure tie in, but should hold for a few months. The forward ends are really wide and flat which may pop the boat up too hard in waves. If I get the boat running ok I can always narrow the mold up before popping out a fresh and structurally sound hull. Attachment 61546Attachment 61547Name:  IMG_3508.jpg
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    mini tunnel boats for sport, now an experimental Sport C added to the fleet.
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    Question

    I know someone else out there has a Sport C or similar tunnel they're working on this winter. What's it look like (without giving away your classified speed secrets)? What are you doing to make it faster?
    mini tunnel boats for sport, now an experimental Sport C added to the fleet.

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    Default Sport C tunnel boat

    Basic shape is done. Gelcoated, then board sanding and hopefully don't need more fairing compound.
    mini tunnel boats for sport, now an experimental Sport C added to the fleet.

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    Let us know how your modification works.
    Dean Hobart
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    Default Sport C tunnel boat

    Does anyone with a tunnel boat have hook on the sponsons? I have a tiny bit (about 1/32") left over from a past test. I was thinking of leaving it for the moment but maybe I should get rid of it while rolled over?


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    mini tunnel boats for sport, now an experimental Sport C added to the fleet.

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    Default Sport C tunnel boat

    Ran more numbers through the TBDP program and it all showed slower acceleration with hook (simulated it using the trim tabs function). Got out the board sander and flattened the sponsons. I still have a little hook in the center pod. For now I'm leaving it. If the motor runs out of water before I spin out then I'll sand it down. Otherwise I'm hoping it will keep the motor a little drier with the big stock gearcase. Maybe next week I'll get in a test lap.
    mini tunnel boats for sport, now an experimental Sport C added to the fleet.
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    Default Sport C tunnel boat

    mini tunnel boats for sport, now an experimental Sport C added to the fleet.

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    AeroMarine Research Jimboat's Avatar
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    Quote Originally Posted by BYOBoat View Post
    Does anyone with a tunnel boat have hook on the sponsons? I have a tiny bit (about 1/32") left over from a past test. I was thinking of leaving it for the moment but maybe I should get rid of it while rolled over?
    Your boat's looking great! Any amount of 'hook' in main running surfaces (sponsons) will normally reduce top speed a little bit. It will also reduce trim somewhat and potentially preclude/delay porpoising, which can be a good thing, but of course, there's the performance degradation to consider too.
    Looking good!

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