NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Awareness
From: Doug Royer
Date: 2003 Apr 23, 10:17 -0700
From: Doug Royer
Date: 2003 Apr 23, 10:17 -0700
All boats are created equal.It's just some boats are created more equal than others.Small vessels are subject to the same physical phenomenon as large vessels.What are the physics of the edge of a prop closest to the hull creating more turbulance and drag than the edge of the prop further away from the hull?I don't know.I don't think I need to know.I am aware of the phenomenon and can plan accordingly to counteract it and that is important.I can't discuss with you guys the physics of this stuff because I'm not versed in physics.If a mariner is not aware of a phenomenon how can he plan to overcome it? Take for instance the area of optimizeing a prop.How many recreational boaters are aware that an optimized prop for a vessel will give better power,maneouverability and reduced fuel consumption?If not aware of it how can one take advantage of it? I will give you an actual test question that was on my 2nd Officers exam."If the pitch of the prop is 26.3 ft. and the revolutions of the shaft is 87,421 revs. in a 24 hr. period,calculate the days advance allowing for a negative 7 % prop slip."What is this you say?This is as an important phenomenon in navigation as getting an LOP from a Celestial object I say.If you are not aware of it how can you take advantage of it?Small vessels can use the same ideas if aware of them.The art of practical navigation encompasses all these ideas not just one or two. The Merchant Marine is run on 2 basic principals,optimazation and money.With optimazation comes reduced transit costs and greater profit margins.Small vessels can use the same principals if aware of them.Optimazation of a track will take advantage of weather,current,wave and wind action and use it to ease or speed the advance.The same is done for avoiding areas that will have an adverse effect on the advance.Speeding up or retarding a leg of the transit to take advantage of calculated conditions further along the track is also a usefull proceedure.A case in point is both San Deigo Bay and the Bay of Fundy.San Deigo has an extremely narrow channel that is subject to high tidal currents.The Bay of Fundy has extreme swings in tidal heights,sometimes 20 ft. or more.You definetly don't want to be transiting these areas in any vessel at the extremes of the conditions.By being aware of the phenomena you can plan accordingly.You don't need to know the physics of the phenomena. So,getting as much info or knowlege as possible and being aware of it and then putting it to use in practical boat handleing or navigation is the essance of what this is all about. I'm so glad these subjects are comeing up on this board to discuss and learn as I think they are every bit as important as the fine points of Lunar Observations etc. I would like to ask a question of the group and in no way is it a criticism.I've just been wondering about it since reading the threads of the last few years.How many of you have done a Lunar observation on a voyage and used it?Please,this is not a criticism.