I'm no expert but I recall an article over the past six months (I think by James Jermain in Yachting Monthly) in which it was explained that salvage rights are calculated on the basis on the amount of danger from which the vessel was made safe.
So, if your engine just blew up while waiting at slack tide for lock gates to open to Cardiff Bay, there is no danger and requesting a tow would not likely incur salvage rights.
If the situation was in a dire sea state and the rescuing vessel (assume that is what it has become) has made risk in effecting the salvage, and to have not done so would have resulted in a reasonable loss, then salvage rights become an issue.
I believe (but may be wrong) that the concept of using your own line has been reasoned by maritime lawyers to indicate that you are still in some semblance of control, so diminshing the "degree" of the rescue.
A simple written document exchanged between skippers MIGHT have the same effect.
Of course, I'm not a lawyer and this could be unreliable advice etc.
You are just about spot on. I would add that I understand there is a precedence that a yacht in trouble a harbour would not result in salvage - say an angine failure in the ebb and too much tide to sail against.
So if you see one of those happening wait until it's past the fairway marker before offering a tow.
There is not much to add to Humperdink's posting although the following might be worth knowing.
You can only claim salvage on tidal waters.
Salvage is always calculated as a proporting of the value of the boat depending on the degree of danger the boat was in.
Courts very seldom award more than 50 per cent of the value of the boat.
Insuranced companies can refuse a salvage claim if it believes the boat was not in sufficient danger.
Incompetency of the crew is a material fact in assessing the level of salvage, so don't make unguarded remarks about your navigators competence.
Do everything you can to show that, despite being in danger, you are as much in control of the situation as you can be; ie use your own warps, keep the engine running or sails set or ready to hoist, and someone on the tiller, form a contingency plan if the salvage, operation comes to naught, make sure your navigation and pilotage are up to date and correct etc.
Don't put out a distress call unless you are actually in danger. Response to a May Day call does, per se, lay you open to a salvage claim (but the RNLI very rarely claims and the Coastguard, as a professional rescue service, cannot). Even a call for assistance - such as 'my GPS is down, can you give me a position' - could be construed as a salvage situation. Borrowing fire extinguishers, bilge pumps, or any other safety gear, could lead to a claim for more than the value of the items.
The salvor can arrest your boat at any time while the claim is unpaid. This applies even if you sell the boat, so the buyer must be made aware of the situation.
Salvage is always 'no cure, no pay'. Make sure both parties understand the basis of the assistance before the salvage operation starts - you may not be in a good bargaining position, but don't agree to paying large sums under duress, if you can't agree a figure make it 'subject to arbitration' - bear in mind the court's 50 per cent of value limit. It may seem unnecessarily gloomy, but it might be prudent to keep a suitable salvage agreement form on board (There is one in the MacMillan Yachtsman's Handbook and I expect the RYA has a specimen version).
Other tips include: don't disclose the value of your boat; inform your insurance company as soon as possible; boats which are performing a legal or professional duty cannot claim salvage (tell that to the professional French lifeboat crews!)which excludes the voluntary RNLI crew who should be given a substantial donation instead (plus pints all round at the local watering hole.
One or two dangerous misconceptions here, so beware;-
1) 'no cure no pay' only applies to Lloyds open form salvage and must be agreed by both parties before a service commences. It is designed to avoid delays and both parties agree to a binding independant arbitration.Even open form can allow a salvor to reclaim his costs in preventing pollution , even if the salvage is unsuccessful
2) A mayday call is mot essencial for a service to be chargable
it is best to establish exactly what service is being offered and what, if any, charge is to be made. Inform a third party as soon as possible, or better still get it in writing.
with 15 years in the towage industry it pays not to take chances! However we are all seaman and i've never made a claim for helping a boatowner out yet.Beware though, our patience is pushed by incompetent owners who may only learn a lesson the hard (expensive) way