a dream of a long narrow planing hull

Discussion in 'Boat Design' started by Sean Duval, May 11, 2019.

  1. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,759
    Likes: 272, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    38 foot boat seems a nightmare to wrangle on to a trailer, and then to trail it any distance. Maybe a seabright skiff hull would be a good way to get the fast troll speed.
     
  2. DCockey
    Joined: Oct 2009
    Posts: 4,371
    Likes: 201, Points: 63, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    How are you defining a "semi-displacement hull"?
     
  3. Sean Duval
    Joined: Mar 2019
    Posts: 26
    Likes: 7, Points: 3
    Location: yuma az

    Sean Duval Junior Member

    Well....38ft boat won't be great fun to trailer that's for sure...
    On the bright side it's a pretty straight run from Yuma AZ to the two locations I generally launch from in san Diego. A little bit of mountain....but soft turns..and reasonable downhill grades. The launch ramp at dana landing will give me a ton of room as its 10 lanes wide....and early before dawn or after sunset nobody uses it much. Can launch 24/7 there and parking your vehicle with boat trailer attached is free.

    I'll gladly give a bit of annoyance in driving to have what I perceive as a want/need on the water.
     
  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,759
    Likes: 272, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

  5. BlueBell
    Joined: May 2017
    Posts: 848
    Likes: 93, Points: 28
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    It's a one-way trip, no return?
     
    Barry likes this.
  6. fallguy
    Joined: Dec 2016
    Posts: 2,133
    Likes: 140, Points: 63, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I have fished a few times where you speak of and you would name the ship 'Stock in Dramamine'. When the 8.5' beam starts to roll; it would be awful. We were out in 2-3 meter seas on the Malahini and about 1/3rd of the people were sick. Malahini is 80x20

    The problem with your concept is you want a long narrow hull why?

    Because you like the way it looks.

    And the sor should start without worrying about the looks.

    You want a trailerable boat for affordable trolling in the South US Pacific. It exists, but not the boat you like.
     
    Last edited: May 15, 2019
  7. Mr Efficiency
    Joined: Oct 2010
    Posts: 7,759
    Likes: 272, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Trailing width restrictions, presumably.
     
  8. mselle
    Joined: Jul 2004
    Posts: 29
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Island Mjoern, Westcoast of Sweden

    mselle Transportation Designer

  9. Sean Duval
    Joined: Mar 2019
    Posts: 26
    Likes: 7, Points: 3
    Location: yuma az

    Sean Duval Junior Member

    Moselle that's a neat looking craft too, and has the lines I was looking for..

    Ok I need to answer questions and ask more...please don't be offended by my questions or answers...I like many who read these forums am learning from you folks who have more knowledge than us on this subject. From what I have read on here I totally understand some of you know way more than I do and have likely forgotten more than I will learn in this field.

    Answers not necessarily in order.

    Yes reason for width restriction originally was based on trailer restriction...then I did some research that apparently has results questioned by some regarding planing hull design of a more narrow persuasion. Initially this seemed like the right answer as it addressed several needs. Though there is some contention regarding this....there appears to be a correlation between fuel efficiency and long narrow planing hulls up to and a good bit beyond hull speed. There also is the slicing effect vs pounding due to how a long slender hull reacts to waves....to me this means when going out to sea as the eastern pacific swell has a significant rise and fall. It appears to me that with sleeping accommodation in the for peak followed by a minimalist pilot house/cabin area that I could easily place the inboard engine(s) outside the cabin...and arrange that area of the decking and hull to provide very good and comfortable access for maintenance (to me extremely important as most boats inboard engine compartments area very cramped and awkward at best.)
    And leave me ample room for a 3 scoop bait tank to the rear and likely a nice insulated fishbox.
    I'm not sure if outriggers will have any damping effect on roll or not.
    The intent is fishing boat 1st which to me means reliable, survivable, and efficient at trolling speeds. Sleeping area is for tired fishermen, who hopefully will be more like me and not suffer from motion sickness. fuel tank placement would ideally be close to center of buoyancy I would assume and as low as possible.
    I could be wrong but the driving/trailering issues on the road wouldn't be much if any worse than towing a large RV type trailer....plan ahead, know your limitations and act accordingly.
    Launching and returning the boat to the trailer I wouldn't see as much of an issue with proper trailer design (I think) provided the operator actually knows what the heck they are doing...and yes I realize most don't. Additionally yes this would be the largest power boat I have owned and operated by a good 10ft....my only edge in regards to this is all my life I have operated both sail and powerboats of varying sizes and in some interesting circumstances.
    To the low long sleek appearance...no I am not looking for appearance for vanity or because I want someone to go "oh wow that's a pretty boat" the dimensions come about out of mission driven requirements...trailerable...enough room...diesel powered...smooth while underway...and efficient while fishing.

    Oops ran out of time...will ask my questions when I have another break at work.

    P.s. thank you all for your input, I note varying opinions and I believe that helps us all understand hull dynamics better.
     
  10. DCockey
    Joined: Oct 2009
    Posts: 4,371
    Likes: 201, Points: 63, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    You may want to check the laws for the states you may drive through.
     
  11. kerosene
    Joined: Jul 2006
    Posts: 1,041
    Likes: 60, Points: 48, Legacy Rep: 358
    Location: finland

    kerosene Senior Member

    I follow with interest.

    I do question the fuel bill consideration in the context if ~40ft custom build.

    Will the potential fuel savings ever matter?

    Of course big engines cost and fuel is heavy - I get tthat part.
     
  12. Dolfiman
    Joined: Aug 2017
    Posts: 1,021
    Likes: 433, Points: 83
    Location: NICE (France)

    Dolfiman Senior Member

    Trailering limits in France (and likely in line with European Union ones, to check) with a usual driving license (named B) :
    *** width max : 2,55 m (/ Loxo 32 : Boa 2,55 m)
    *** length of the trailer + its load < 12 m (/ Loxo 32 : Loa 9,5 m)
    *** total length (car + trailer) < 18 m
    *** total weight (car + trailer) < 3500 kg (/ Loxo 32, twin motors : 1750 kg)
    *** for a total weight < 4250 kg , you need an additional formation (named B96)
    *** for a total weight > 4250 kg, you need another driving license (BE)
    Le remorquage sur route de son bateau à moteur https://www.paruvendu.fr/auto-moto/I/Le-remorquage-sur-route-de-son-bateau-a-moteur-i13633
    2013 : La réforme sur le remorquage en détail https://www.permispratique.com/2013-La-reforme-sur-le-remorquage-en-detail_a128.html
     
  13. Sean Duval
    Joined: Mar 2019
    Posts: 26
    Likes: 7, Points: 3
    Location: yuma az

    Sean Duval Junior Member

    Thank you guys for your feedback and thoughts.

    Well now to my questions for you folks in the know.

    I have heard the "will roll awful bad" a few times...
    This brings up the question...does the length have an effect on the roll? As in would a 20ft boat 8ft wide roll less than a 40ft boat 8 ft wide...assuming center of gravity was the same ratio wise and such? My thought on this is that the roll should be the same for both hulls, but I don't have the math or experience to back this up...and it would seem to me under power this wouldn't be so much an issue than if adrift in with the swell to the beam.

    Am I way off on my thinking?
     
    fallguy likes this.
  14. DCockey
    Joined: Oct 2009
    Posts: 4,371
    Likes: 201, Points: 63, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Start with a 20 foot design and stretch it to 40 feet by scaling by a factor of 2 in the length only, beam and height stay the same. Keep the "density" constant so the weight increases by a factor of 2 and the CG height stays constant. Then the resistance to a heeling moment doubles. The roll period stays the same. The moment induced by waves from abeam would increase by approximately a factor of 2 so the roll magnitude from waves would stay about the same.

    So why the common knowledge that narrow boats roll more than wide boats? Probably several factors. One is folks are used to comparing boats of the same length and different beams, not different lengths and the same beam, an for a given length a wider boat will be stiffer. Another is longer boats tend to be taller which may mean the CG is higher and that leads to more rolling.
     
    fallguy likes this.

  15. DCockey
    Joined: Oct 2009
    Posts: 4,371
    Likes: 201, Points: 63, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    The effective limit on vehicle width in the US without "wide vehicle" permits is 102" / 2.59 m. Maximum combined tow vehicle and trailer length without oversize vehicle permits varies by state in the US. Maximum vehicle weight with a standard non-commercial driver's license varies by state. Many states have a maximum trailer weight of 10,000 lbs without a CDL (commercial driver's license). Types of Driver's Licenses - AAA Digest of Motor Laws https://drivinglaws.aaa.com/tag/types-of-drivers-licenses/
     
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.