howardang

The trouble is that this diagram from Castlemarine ignores the major factor about "propwalk" altogether - namely the more disturbed water nearer the surface as I tried to explain earlier and which is the main cause. This diagram has been quoted before and I think I even got into correspondence with the writer because his basic premise is wrong, namely that with a zero shaft angle there is no prop walk. This is patent twaddle! I think an easy way to try to explain how prop walk works is to think about a propeller turning righthanded with the waterline at the propeller hub level; in other words with only half the prop immersed. The blade as it enters the water pushes the stern across to starboard because the blade at the top of the rotation is only pushing against air therefore nosideways force to speak of. Now, progressively ballast the boat down and the bottom blade will still have this push to starboard, although it will be countered by the increasing effect of the upper blade at the top of its rotation as the water deepens. Eventually, when the propeller is totally submerged the two blades (top and bottom will generate opposite forces which, however, are not equal, because the top blade is in less dense water than the bottom (because of the agitation which is more pronounced at or near the surface) hence the "prop walk" effect is still more pronounced to starboard than to port. Now, increase speed, and the faster the prop is going, the less the effect is in relation to the axial thrust which is progressively increased. Howard

As I have commented elsewhere, in my opinion the theory about prop walk etc being caused by trim angle is a fallacy, and if you draw it out the change of angle from a full water tank to an empty one, using a boat typically 50 ft long with a 5 inch change of trim would be hardly noticeable. Most vessels on the canals and many elswhere have prop shafts which are parallell or nearly so to the water surface) and yet suffer the effect. I would also say that, in my experience, every propeller acting in water will generate an element of transverse thrust unless it is either in a tunnel (many lifeboats have this arrangement which I'm sure Carl will be familiar with) and props in Kort nozzles,where the thrust generated is axial. The prime cause of transverse thrust, which has been taught in ship and boat handling circles since Adam was a lad, is that the bottom blades meet more resistance when turning than the top blades. This is caused by the greater churning effect of the blades nearer the surface, and therefore the bottom blade meeting more resistance with the more solid wall of water, generates a sideways force which we call various things. I call it transverse thrust because I first learned the term relating to ships, but like others I have come across prop walk, paddlewheel effect etc. The net cause, however, remains the same - to cant the stern to starboard when going ahead with a righthanded propeller and vice versa when going astern. There are other effects which make themselves felt in the rudder/propeller area but which are small in effect c ompared to transverse thrust. Howard

I'm sorry, Carl, but the angle theory just doesn't stand up. The effect of transverse thrust, propwalk or whatever you want to call it certainly can be felt with a prop shaft at zero angle. I would think 99% of boats on the canal have their prop shafts at or near zero angle and yet they experience it. In fact the vast mojority of ships fall into this category too. As far as aircraft are concerned, isn't the similar effect they experience caused by the gyroscopic effect of the airscrew spinning at high speed which causes precession at right angles to the direction of thrust. Howard

I suppose it depends where you come from! It's been called by its proper name, 'Transverse thrust', almost since propellers were invented. Each to his own, I suppose. The thing with PWE or TT or PW (you choose) is that it can be used to advantage because once you know which way your prop rotates, you can allow for it, or use it to help in manouvering. A prop which rotates clockwise when going ahead (right-handed) will push the stern to starboard and therefore the bow will go to port unless corrected. The opposite when going astern. Vice versa for a Left-handed prop. HTH Howard

The main reason why resistance is increased is that the shallower the water, the more the effect of squat, which causes the boat to increase its draught and it therefore needs more energy to push the deeper hull through the water, which is what I was trying to say before but not very well! HTH Howard

The nearer the boat is to the bottome the more the effect of water flow to the prop is felt as resistance to forward motion, because the flow has nowhere else to go and causes drag. Howard

Try making your own emergency rope ladder - easy to make, handy to stow and quick to deploy hanging over a suitable mooring dolly. The following animation makes the construction clear. http://www.marinews.com/Rope-Ladder-782.php HTH Howard

This is what he was asking about - if a boats mooring rope is passed through one end, wrapped aroun the snubber a few times and them fed through the other end, and then made fast in the normal way, it absorbs some of the strain when the rope comes under tension. http://www.marinemegastore.com/product-product-ECS_3980.htm Yes I was aware of the other definition of snubber, but thanks anyway. Howard

No, what you are describing is a snubber. Howard

These three sites may help. http://www.ownerships.co.uk/ http://www.boatshare.co.uk/ http://www.carefreecruising.com/ I have shared a boat for a number of years via the most popular scheme - Ownerships - and can thoroughly recommend it. HTH Howard

Rule 20-b of the col regs say "...In a vessel of less than 20 metres in length the sidelights may be combined in one lantern carried on the fore and aft centreline of the vessel' HTH Howard Anguish

Ellen McArthur passed her Yachmasters certificate at either 17 or 18 but the RYA were reluctant to award her with it until she got some sea time, despite the fact that she was, by then, helping to instruct others... so she set off and sailed single handed around the UK. She got her certificate when she finished the trip! Howard Anguish

.........I don't think the NUS would care less - however the RMT might! Howard

It might be false economy not have a survey done for your peace of mind, and if the surveyor is worth his salt he might find enough points to make his fee worthwhile - you may be able to reduce your purchase price by the amount needed to rectify any items for example, and indeed your insurance company and/or finance company might insist on one. A 2 year old boat may be in pristine condition but may on the other hand have a number of defects requiring attention which may not be obvious at first glance. Howard

I agree completely, Carl. The tragedy is that the families left behind have to live with the fact that these people lost their lives through an act of gross stupidity and despite being warned repeatedly. Howard

South Ferriby Marina is at http://www.southferribymarina.com/ Howard

Although it would be perfectly possible to base such a boat in Hull I would suggest that if you want to explore further afield regularly then Goole or Thorne would be a better bet (and possibly cheaper - certainly than Hull Marina) Depending where in Hull you live you can be at the boat within say 40 minutes. Hull Marina would give you good access to the river 3 hours each side of high water, but Beverly Beck is slightly more fraught. In either case you would be much more weather dependant if you were based in Hull - the Humber can be just as bad as the North Sea at times, especially in a wind against tide situation, and not a very nice to be for a small boat in those conditions. Hope that helps Howard

Halcyon - happy memories! The name of the first vessel I went to sea on - seasick for a week! Howard

As usual, nothing is simple, Tidal! If you look at the BW Bye Laws they don't actually say that they are following the col regs. However, the wording which relates to steering and sailing rules, lights etc bears close similarities to the pre 1973 col regs ( the ones I was brought up on!) with obvious additions where necessary to include such things as dropping towropes when two towed boats approach each other in a canal for instance. No mention of CEVNI. The only copy of the Bye Laws I can lay my hands on is the one on the web site as follows http://www.hnboc.org.uk/ Look in downloads for the Bye Laws - they appear to be an old copy but I understand that they are still current. HTH Howard

Sorry Tim, but porthole is very much a marine word. You're quite correct to describe it as a scuttle, but only on a Royal Navy ship. On a merchant ship it is definately called a port or porthole (the word scuttle is seldom used) and a deadlight is the brass or steel cover which fits over a porthole when it is situated below the freeboard deck to prevent any water getting in in case the glass is broken. Doors in the sides of a ship through the shell plating for access to tween decks for cargo working are referred to as cargo ports or sometimes gun-port doors. Howard Anguish

The link to the consultation document is here. http://www.britishwaterways.co.uk/images/K..._April_2008.pdf All documents such as this can be found on the BW web site - "accountability" - under "consultations". HTH Howard

Sorry to sound negative but it is difficult to teach boat handling on a discussion board. Has she got someone who can show her the rudiments on board her boat? Failing that, she should take a course in boat handling - there are many to choose from. However, if she is unsure of how to moor in the conditions you describe , surely she shouldn't be moving the boat in the first place! Howard

This might be helpful: http://www.boatus.com/boattech/casey/34.htm HTH Howard

Wieght of the boat vaiies with length and the heavier the boat the biger the anchor. Howard