economical coastal cruiser

Discussion in 'Boat Design' started by sandy daugherty, Feb 11, 2010.

  1. Pierre R
    Joined: May 2007
    Posts: 461
    Likes: 32, Points: 0, Legacy Rep: 458
    Location: ohio, USA

    Pierre R Senior Member

    Tom I certainly was not trying to slight your BJ series of boats. They look pretty nice to me for what they were designed for. I can see trailering one to take a vacation on the Erie Canal, the Tennessee river system or the ICW south of your present position. Maybe even live on the St. Johns river in the winter. I would expect that I could build the BJ 28 for in the neighborhood of $20k with outboard. Something like Gerr's DR 28 would be more in the neighborhood of $90k.

    That said there is a world of difference between the BJ 28 and the DR 28. Those contemplating building either should be aware of the differences.

    I will keep you web site saved. I run into a lot of folk for whom the BJ series would work well.
     
  2. sandy daugherty
    Joined: Jun 2008
    Posts: 132
    Likes: 4, Points: 0, Legacy Rep: 52
    Location: Annapolis, MD

    sandy daugherty Senior Member

    Since I like to see all the sights from the water, my choice of RVs would be severely limited (or very expensive) To tell the truth, I intend to continue sailing my PDQ 36, and was inspired to start this thread with the thought that it would be nice to go to the Miami Boat Show via the IC, but it would be better to do it at more than 6 knots and without a full set of foulies. So I started looking at small trawlers on the internet. Plastic rocket ships are out because I'm green and cheap.

    I have to thank all of you for intruducing me to a world of new concepts and practices. I've been bit and I'm going to put at least one foot on the dark side. I gotten to "quarter-beam buttock lines" in Dave Gerr's book, and I am hanging on, if reading slower. So Tom Lathrop's BJ Glider is "veeerrryy intelesting" to say the least. Where can I read more?
     
    Last edited: Feb 22, 2010
  3. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 117, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    Pierre, No slight detected or taken. It is only because of lengthy recuperation from heart surgery that I am hammering away at the computer so much and perhaps dominating this thread way too much.

    You are certainly correct that the BJ28 and the Offshore 28 are very different in just about every way. Either is better in its own element than the other. I do have one quibble. I doubt that the materials building cost of either is much different. What difference either might be built for is more closely related to the level of finish desired and interior elements included than the basic materials. In any case it would be more than the lower figure for the BJ28 and far less than $90K for the DR28. I don't know where that much money could be used. Cheers!
     
  4. Pierre R
    Joined: May 2007
    Posts: 461
    Likes: 32, Points: 0, Legacy Rep: 458
    Location: ohio, USA

    Pierre R Senior Member

    Ah Tom, I misstyped. I was thinking the DR 34 Northwest not the DR 28 at a cost of $90k.

    What do you estimate is the cost of materials for the BJ 28 and what kind of time to you estimate for construction to a medium commercial finish?
     
  5. graftonian
    Joined: Aug 2009
    Posts: 14
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Grafton, IL

    graftonian Junior Member

    Tom,
    Good to see you up and about. Wishing You a speedy recovery.
    Duane
     
  6. u4ea32
    Joined: Nov 2005
    Posts: 416
    Likes: 14, Points: 18, Legacy Rep: 192
    Location: Los Angeles

    u4ea32 Senior Member

    OK, maybe I'm missing something. I see the 8K lbs displacement as a maximum, not a minimum nor a target.

    If we do the same as Tad, and parametrically explore the possibilities, it sure looks simple to me.

    Let's say it does need to be 8.5 feet wide, and light. That suggests a hard chine shape, which suggests a planing hull. So let's use the old and very well proven Crouch method.

    http://www.go-fast.com/boat_speed_predictions.htm

    Gasoline: 10hp/gal/hr, Diesel 20hp/gal/hr.

    So for gasoline power, we need 12 HP. For diesel, we can use 24.

    Let's assume a well designed, stepped bottom, so the Crouch number is about 250.

    That allows a weight of 5208 lbs uses 12 HP to go 12 mph.

    Now, to be fully planing, as one must be for the Crouch equation to work, you've got to have very light bottom loading.

    What is the bottom loading required to plan at, say, 9 knots? It must be computable, and its certainly possible as there are plenty sailing dinghy classes that plan at less than 9 knots.

    Building a 40 foot 15 degree V bottom that weighs 5000 lbs is trivial: epoxy glass and nomex yields a 0.5 lb per square foot finished boat that is mighty tough (again, plenty of racing dinghys are this weight, but so are STP 65 racing yachts -- but they are carbon not glass, but have ENORMOUS loads). The entire hull and deck and interior structure for the STP 65 Rosebud, built by Westerly Marine in 2007 of carbon, epoxy, and nomex, weighed 2200 lbs!

    Let's make the planing requirement simpler: If the engine is diesel, we can go 17 knots with the same 1 gallon per hour, same displacement of 5208 lbs. A shorter hull with more conventional loading will plane flat at 17 knots.

    In other words, reduce the displacement, make it plane with an efficient (stepped) bottom, and the 12 mpg target is not tough to hit. You can't hit it if you try and go 30 knots, but if you get fully planing at low speed, you can.
     
  7. Willallison
    Joined: Oct 2001
    Posts: 3,590
    Likes: 130, Points: 0, Legacy Rep: 2369
    Location: Australia

    Willallison Senior Member

    Wow - that's an interesting conclusion...
    A 40 x 8.5ft, 2,300kg boat that will plane at 9 knots, using 12hp to do 12....
    Good luck with that.....
     
  8. Willallison
    Joined: Oct 2001
    Posts: 3,590
    Likes: 130, Points: 0, Legacy Rep: 2369
    Location: Australia

    Willallison Senior Member

    Apology for the sarcasm....
     
  9. TollyWally
    Joined: Mar 2005
    Posts: 774
    Likes: 26, Points: 0, Legacy Rep: 423
    Location: Fox Island

    TollyWally Senior Member

    Might I be so bold as to suggest that one problem with a 40 foot hull with low enough bottom loading to plane at 9 knots with 17 hp no matter how exotic the hull materialis is keeping that 40' hull free from all the accumulated gear that a cruiser naturally collects.
     
  10. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 111, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    40 foot hull with low enough bottom loading to plane at 9 knots with 17 hp

    Would be interesting to be able to compute weather taking 75% of the hull weight in the box keel canoe body would lower the plaining bottom loading enough to get even greater efficiency.

    Either a higher cruise or smaller fuel burn? But I sure cant do the math!

    FF
     
  11. Pierre R
    Joined: May 2007
    Posts: 461
    Likes: 32, Points: 0, Legacy Rep: 458
    Location: ohio, USA

    Pierre R Senior Member

    I can understand wanting to be super green but so often lately this seems to be trumping practicallity in these discussions.

    Generally speaking, a boat getting 4 mpg will not be able to burn enough fuel annually while traveling north and south along the US Eastern Seaboard to offset what even modest living on land will produce in terms of energy use. By moving aboard you are almost always greener than if you live on land.

    A nice boat that will not trash you when it hits a boat wake, not be uncomfortable and unsellable can be made to do what you want for around 4 mpg. Even at 2-3mpg you are still plenty green enough.

    I know that we are a bunch of thinkers and dreamers but when the money hits the table most of us don't approach the impractical things discussed here.

    I know that I play these stupid numbers games with my own boat. If I slow down my own boat one knot off hull speed I can increase my mileage by a whopping 30%. Think of all the money I can save in a day. In a 10 hour day I will burn three gallons less but also travel 10 miles less. Now over the same distance that translates to about 2.1 gallons less. Wow, I am saving $6.00 at todays prices. That is 60 cents and hour. Now on a 4000 mile annual basis I could save and additional $489 and only pay a 133 hour penalty.

    So after all these calculations, what do I say to myself and do? Oh piss on it. run the damned engine at 65% power and pay the additional 60 cents an hour penalty you frikin greeny cheapskate . I am flying at 6 knots and poking at 5 knots. I'm not on land so my energy usage is still less even at the whopping 30% increase in dinosaur juice. My fuel bill is around 7% of the budget even at the higher fuel burn. I can burn $489 in the car in less than a couple of months. Such is the silly games I often play with myself.
     
  12. sandy daugherty
    Joined: Jun 2008
    Posts: 132
    Likes: 4, Points: 0, Legacy Rep: 52
    Location: Annapolis, MD

    sandy daugherty Senior Member

    Much of the Waterway is speed posted, as low as 6 knots. Long stretches cross some moderately snotty conditions of steep chop in shallow water, such as Pamlico sound, or pounding down the Delaware Bay. Is a stepped hull such a good idea there, with dishes in the sink?

    Oh, Pierre, thy lash doth sting. Your point is taken, with a heavy seasoning of grumbling. So I have to quit pretending to be all that virtuously green. If that were really my goal I should ride a bicycle to the train, and sleep under the stars. Or just stick to sails and live on raw fish and bilge-grown bean sprouts.

    Not.

    I'm too old, I creak, and I worked 45 years to afford a little ease in my dotage. So its back to the wishlist to decide how much a sufficient level of comfort weighs. There should be spreadsheet where you simply check off what you know you need to be comfortable, that would calculate the weight, then the size and shape of right boat.

    Do you designers have to go through this with every customer that comes along?
     
  13. TollyWally
    Joined: Mar 2005
    Posts: 774
    Likes: 26, Points: 0, Legacy Rep: 423
    Location: Fox Island

    TollyWally Senior Member

    "So its back to the wishlist to decide how much a sufficient level of comfort weighs. There should be spreadsheet where you simply check off what you know you need to be comfortable"

    Those are both damn good ideas.
     
  14. Pierre R
    Joined: May 2007
    Posts: 461
    Likes: 32, Points: 0, Legacy Rep: 458
    Location: ohio, USA

    Pierre R Senior Member


  15. u4ea32
    Joined: Nov 2005
    Posts: 416
    Likes: 14, Points: 18, Legacy Rep: 192
    Location: Los Angeles

    u4ea32 Senior Member

    Will, your Graphite design looks close to what's asked for. The 4nmpg at cruise: what speeds?
     
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.