Cutting a Mono (dinghy) in half to make a cat

Discussion in 'Powerboats' started by sabahcat, Apr 30, 2012.

  1. sottorf
    Joined: Sep 2007
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    sottorf member

    The asymmetrical bows will not be a show stopper. As you point out there are quite a number of boats out there which have such asymmetrical hulls. Compared to the monohull, the directional stability will not be as good but still functional. If you want to improve it further then fit a semi-symmetrical bow section.

    Given your boat is small and you have an outboard skeg in the water, it is also less likely to be as serious as on larger boats. With a bit of trials and error you could make it work. Don't be put off by the negative comments here.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    If the idea was a sound one, it would have been adopted for the mass market, given the attraction of a more stable platform that it provides, but it hasn't and I'd say for the reasons discussed.
     
  3. tunnels

    tunnels Previous Member

    Cut the boat and unsert a tunnel !! Now you have a tunnel hulled boat !!!! Do you understand the differance between a tunnel boat and a catamaran !! They are simular with two hulls but thats where the similarity ends !!! The behave differant to each other . A tunnel boat is breed from a race boat and loves to go fast !! A cat id a stable plateform and much more stable that a mono hull . so do you want to go fast and be stable of do you want a fishing boat that sits resonably stable !.
    The tunnel is designed to let air between the two hulls and produce a percentage of lift at speed from the cushion of semi pressurised air the shape of the tummel os im portant also is the width and volumn of the tunnel . if you make the tunnel to tall you loose the effect if to shallow then theres nothing to make it work go look at some tunnel boats go have a ride in one , now try a cat and see what the differance is . Twin out boards at the call of the day but tunnels will still go well on a single motor ,Tunnels like to go so dont underpower them .
    The tunnel i used to make were 5.1 mtrs long (in the picture )!, a pair of 40 hp was hopeless and struggled just with one person , a pair of 55hp suzuki was nice to drive, fast and go any where !!, a pair of yamaha 60 hp and was fantastic !! just a small increase made a bigg differance !! a pair of 70 hp and was boaderline on being dangerous !! so the power range for a tunnel is tight and not much to playwith !!
    I always wanted to try the 4 cylinder mercury 100 hp fishing motor as a single motor but was during the down times and the company went bust !!
    A single 90 hp ,25 inch long shaft on the same hull but as a open fishing boat was a smooth boat and economical and pleasent to drive and could handle almost any kind of a sea with ease !!
    Tunnels track beautifully in any kind of sea in any dirrection with just one finger steering !! they are really user friendly !!
     

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  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Well, you'd then have to wonder why they haven't become the design of choice for small power boats. Saying they track in any kind of sea in any direction, is a pretty bold assertion.
     
  5. tunnels

    tunnels Previous Member

    The small boat i have posted in the photo was what i used to make . when you were driving anywhere you always forgot how small the boat actually was !
    I have been out in the breaker line and sat sideways and the waves just rolled under the boat ! going with the sea or against the sea you dont even have to touch the wheel !! Just point and go !! it tracked overal in a straight line !
    Have you ever driven a tunnel before ??
    its not a cat !its a tunnel and they are not the same !!
    The same company made a 21 footer as well and that was a awsome boat !! there were only two of those boats ever made and both ended up going to Hongkong ! this boat with 2 140 hp yamahas used to fly and in a one metre harbour chop went straight over the top like it wasnt even there .
    There was also a 30 footer and thats the picture of the boat flying !! this boat had a pair of 200 yamahas and was boat of the boats show the year it was built and launched
    Note tunnels not cats they are differant !!

    When my time is up here in china and i return home to nz i intend to make for myself a tunnel almost exactly the same but a 6 mtr cabin boat . All glass from Flat panels taped together !!as it will be a one off made on the lines of stitch and tape concept !


    People that continually fight with there boats need to set them up properly and learn what the boat will handle and get to know it better !!.
     

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  6. tunnels

    tunnels Previous Member

    Yes it is a bold statment and given the choice of any mono made of the same size i would back a tunnels of That particular design any time 110% !!!:D:p
    Public acceptance is the biggest stumbling block to over come when you are a manufacture .:confused:
    We are really just sheep and keep flocking together !!::eek:
     
  7. tunnels

    tunnels Previous Member

    The sad end of a beautiful begining !!

    Since the company close down and sell off of all moulds and equipment the 5.10 went to some other place that completely did not know what they had bought !
    Added a meter so was 6.10 ! added a cabin that looked like a apartment block and a pair of big motors !! tha boat was completely out of balance
    I saw it at one boat show and i asked about it and was told it was just a stable fishing boat !! thats it end of story !!:mad:
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    What happened with directional stability with a steep, stern quartering sea ? Mayhem ? Hard to believe it wouldn't be ducking around somewhat.
     
  9. tunnels

    tunnels Previous Member

    Tunnel are like running on rails they go where you point them and keep going till you turn the wheel !! The key is set up of the whole boat and understanding the boat you are driving !! The company i worked for i learned more i one year working there than i had learned in 15 years about setting up and what makes a boat tick so to speak . Its all unwritten knowledge and mine came from offshore powerboating guys and race boat designers and builders that were tops at what they did .You watch ,look and absorb knowledge they are giving you and if you ask stupid questions you shouldnt be there !!!
    If you have a problem with boats doing strange things its a combination of things starting with the driver , the way its been set up and the way the boat is loaded !!
    Every boat is differnant!!, no two even from the same moulds ever perform exactly the same !!
    Its like they have a souls of there own and until you have done lots a seat time and know your boat intermitly then you will always be fighting and wondering why does it do that ?
    And if you cant read the sea conditions and you dont know your boat and get yourself into dangerous situations you better up you life insurance for the family because one day you wont be coming home . :rolleyes::cool::cool:
     
  10. sottorf
    Joined: Sep 2007
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    sottorf member

    From your pictures, I can see why you do not pick up directional stability problems - the highly raked stem and forefoot design. Nice design.

    The important difference between tunnel hulls and catamarans is the tunnel height. Tunnel hulls have a very low height in order ot generate aerodynamic lift in ground effect. This implies you are not going to run them in bad seas: all planing hulls will fly over short steep chop like that of HK harbour with ease and their speed will be higher than in calm water in many cases. The problem comes in when the wave length is greater than half the boat length. The tunnel hull will slam like crazy in such conditions and be forced to slow down. A cat will maintain speed better in such conditions and needs to consider directional stability differently.
     
  11. tunnels

    tunnels Previous Member

    How many tunnels have you built , set up and driven ??

    The tunnel hull will slam like crazy in such conditions and be forced to slow down
    Sorry i dont know what or how you got that idea .Slamming never happens with these paticular boats , its the differance between jumping onto a conrete floor from 6 foot up ,to jumping on the same floor with a thick spong sports matt from the same height . they dont slam at all !!! because of the cushion of air between the two hulls . The shape of the tunnels roof and the width is absolutly critical !!! there is a unwritten formular that works but stuff up the shape and it will ride harder . Only once in the whole day did it sneeze and cough water out the front of the tunnel as the guy was almost stopped as a wave rolled under the boat . Get the shape right and its heaven!!
    This little 5.1 metre could run rings around the 21 foot mono deep vee we were using as a camera boat in the same conditions with a 200 merc on the back !!Once we got over the bar coming back into some very confused and fairly rough water the tunnel left the mono for dead and all we could do was hang on for grim death and play catch up a couple of miles up the harbour where the tunnel was waiting for us .
    In a ocean swells and rolling breaking waves the tunnel was like a jet ski and handled it unbelievabley well surprise to all 6 people that were there . One person was a yachty and had never driven a power boat before and his first run over the rough had a beaming grin from ear to ear . Running along the trough of the waves and up at a slight angle and over the top and down the other side out of sight was the thrill of the day and everyone had a go ! the mono at the same speed doing the same thing was not a good boat for that part !!.

    I love these tunnels and size for size no mono or cat can match them or even come close !! :p
    i have been messing with boats since i was 12 years old and designed my first fullsized boat while still at school , i had to wait a couple of years till i started work to be able to build it the passion and joy of being on the water even sailing has never deminished ever !! Im 68 in a couple of weeks and cant wait to get to nz again for 2 weeks next year to get my own boat out of the shed , a 14 foot with a 115 yamaha and goes really quite well when its trimmed out with air liftting the hull and theres no spray coming out the side !!! makes you eyes water and the wind tugging at you hair !! after loosing 4 hats i dont wear them any more !!.
     
    Last edited: May 13, 2012
  12. tunnels

    tunnels Previous Member

    matter of interest !!

    We always made a point of making the back end of the boats nice and tidy and clean looking because thats the part all other boaters ever saw :p
     
    Last edited: May 15, 2012
  13. sabahcat
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    sabahcat Senior Member

  14. waikikin
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    waikikin Senior Member


  15. BobBill
    Joined: Oct 2009
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    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    I moved to an area that was void of lakes and found sailing to be too occasional to be worth the time for my family. I opted for period of powerboats.

    One of these boats was a classic, a 66 PowerCat, which was a symmetrical hulled catamaran. It sported twin 80s, although it was originally built for 60s.

    The boat ran straight line fine, and turns were best navigated with the engines.

    Sadly, the engines were not counter rotating, so one turn was easy, the opposite was a bear.

    I cannot sat how one engine would have worked...

    Not as large a boat as the one above but big enough with 8 foot beam. it was roomy and fun and did not pound, except when it went airborne and landed and more or less stopped, except the stuff in the boat.

    Lots to consider...

    Am back to sailing, and do not miss the bother of the power boats, by and large, including the cat.
     

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