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grandbanks

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  • Website URL
    http://www.saltyjohn.co.uk

Profile Information

  • Location
    Lancashire
  • Interests
    Boats, travel, reading, writing...
  • Occupation
    Engineer
  • Boat Name
    Minnie
  • Boat Location
    Lancaster Canal

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  1. Hi, I hadn't noticed that reference; it's a bit odd because Metz in the USA never refer to the gain of their own product but in that case have used it to describe a generic 54" antenna. We do quote gain over here, but always with the "i". The PL259/S0239 connection is used by most of the manufacturers for boat whip antennas of this type. We've been using it since 1977. So, conformity with the industry norm is probably the most compelling reason it has persisted. We recommend that the joint be covered with a silicone self fusing tape - this is easily removed and leaves no sticky residue - but I have to say that I've seen many applications where no tape has been used and the joint has not been compromised in any way. My own ketch had an un-taped joint for over six years and when we finally took the mast down there was no corrosion or water ingress. I suppose the quality of the plug and socket helps. Still, I would always recommend taping the joint. We also recommend tinned and stranded conductors in the coax cable in order to prevent corrosion and metal fatigue when flexing. One of the reasons for using the old PL259 on boat applications, they are often use with a barrel connector to make an intermediate join, is that they have great mechanical integrity. Also, they are more easily fitted by the layman than some of the other types. John
  2. Hi Nick, No, we don't 'conveniently omit the second, all-important "d". We use dBi as the reference on our Metzeurope site and on our Salty John retail site. dBi, gain over isotropic, is the standard reference in the marine industry. dBd, gain over dipole, is used more often by CB'ers. If you can find, on a Metz or SJ ad, a reference to gain that does not include the all important "i" please let me know and I'll have it changed. Of course, some retailers who stock the Metz may use their own text and we have no control over that. As you know, a high gain is not necessarily better than a low gain. I'd prefer to describe it as broad beam (low gain) or narrow beam (high gain) to make the concept easier to grasp for the general public. On a boat, especially if the antenna is located high up, you don't want a high gain, narrow, radiation pattern because as the boat rolls the signal will be pointing at the sea or the sky and not at the horizon. A broad, lower gain, pattern will always have some portion of the radiation pattern pointing at the horizon. I have only felt the need to clarify this because you singled out Metz for criticism, somewhat unjustly in my view. The Metz Manta is a superb VHF antenna, the only one offering a lifetime warranty, and used by US and UK search and rescue services.
  3. Yes, Bob, you can use a any mag mount. Get one that has a 16mm threaded male connector that will screw into the SO239 socket in the base of your antenna. Your antenna may have a barrel connector screwed into the SO239 socket in the base of the antenna, in which case just unscrew it. The mag mount should have a cable terminating in a PL259 which screws into the SO239 socket at the back of your radio. The length of the cable from antenna to radio is not critical and you don't need to worry about ground planes. You don't need an SWR meter.
  4. You may not have a problem. Believe it or not, these switches won't work in clean fresh water. They need some level of contamination to operate. Also, they have an 8 second delay before starting - which you noticed.
  5. If all the boats on the system were laid end to end you could walk from Liverpool to Birmingham without getting your feet wet. And probably meet some nice people along the way.
  6. Locking must be a tough application for any line. Both nylon and polyester three-strand are the most widely recommended lines for mooring; nylon has a lot of stretch, good UV resistance and abrasion resistance; polyester three-strand has less stretch than nylon and a bit more abrasion resistance - otherwise very similar in those features that we need in boating. I'd be happy with either. Polypropylene has only two virtues - it is cheap and it floats. Otherwise I wouldn't have it on my boat. It has very low UV resistance (but then, I suppose, we have low UV in this country!), it has low abrasion resistance and it is nasty, shiny stuff that doesn't hold a knot. Dyneema/Spectra/UHMWPE are all high modulus polyethelene lines. These lines have the highest strength to weight ratio, so you can use a smaller diameter line should you wish, they are not bad to handle but they don't hold knots well. They have virtually no stretch and are particularly suited to control lines and halyards on racing yachts. Personally, I'd go for nylon or polyester three strand. Perhaps nylon would have the edge for mooring in ocean based marina environments where there is likely to be a lot of movement, so the stretch is important, but I find polyester is less likely to go stiff, and gain less weight, when constantly wet.
  7. Or: Whilst I don't agree with dangling, I will defend with my life your right to dangle.
  8. There is a very expensive difference between a RO purifier and a RO desalinator. Ther former is what it's name implies and uses relatively low pressures, 50 psi perhaps, to produce purified water from ordinary tap water, (and fresh canal water presumably), and can cost as little as £100. A Reverse Osmosis Desalinator, or 'watermaker', uses pressures in the order of 800 psi to produce fresh drinking water from seawater and they start at around £1500. This is the type of unit used by 'blue water' cruising boats that travel to places where water is a precious commodity, and hauling water from a shoreside tap to an anchored boat is a chore.
  9. There's a boat on Chesapeake Bay (USA) called 'The cunning linguist', which I thought was clever. It is rumoured that it's owned by a professor of languages at a Maryland university.
  10. Halyard Marine are specialists in this field: http://www.halyard.eu.com/NoiseVibrationRe...nMaterials.aspx
  11. I haven’t experienced our own waterway system yet but I once took a GRP sailboat from Galveston, Texas, to New Orleans via the Gulf Intracoastal Waterway, one of America’s busiest industrial waterways. The journey took ten days and we were cheek by jowl with barge ‘tows’ comprising, sometimes, 3 barges wide by 3 long. They are actually pushed, not towed. We also encountered ships and even an oil platform destined for the gulf oil fields! When the ‘tows’ are really moving along great spumes of white bubbles are formed in the spaces between the barges. I asked a barge captain what caused that and he said “It’s crushed fiberglass from the little sailboats we run down”! There are two major locks, the Harvey Lock and the Industrial Lock, which connect the ICW to the Mississippi River and the Mississippi to Lake Pontchartrain. We went through the Harvey lock completely alone, it made me cringe at the thought of the cost to the Louisiana taxpayers of our transit, and for the Industrial lock we were ‘hip towed’ by a huge tug. It was very intimidating to be constantly in the presence of massive steel vessels that could crush us like an egg, but it was an experience I wouldn’t have missed for the world.
  12. So, it's slow speed handling and tracking that's enhanced by the additional rudder area. I can understand that. I suppose the typical canal cruiser has quite a flat bottom in the interests of minimal draught and, therefore, little to aid directional stability. The added rudder area would help this. My boat, although only 2' draught, has a short keel running for at least half the boat's length which provides good tracking; I may get away with not having to enhance the steering ability of the outboard - it remains to be seen. This transformation of a traditionally styled sailboat to a powerboat, and one suitable for canal cruising, is proving to be an interesting project!
  13. I've noticed that many cruisers with outboard motors add additional rudder area to the drive leg, aft of the prop. The area added to a 10 -15HP motor is around 1 square foot or so. Does this make a difference to handling? I've always thought that an outboard steers very effectively simply by directing the flow from the propellor and am surprised that this added rudder area makes a difference. My boat has an outboard motor on one side of the transom and a tiller operated rudder in the centre. That's because it started life as a sailboat. I'm planning to remove the rudder and move the outboard to the centre line and use it to steer. The rudder was necessary when the boat sailed, obviously, but I was hoping to steer just with the motor now it's a power boat. Any thoughts?
  14. An internet supplier of uncommon, but tried and tested, boating products.
  15. Thanks, that's what I was looking for. I'm designing an awning frame to go over the open cockpit of my unusual canal cruiser and I want to be sure it will fit through most bridges.
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