Re: Furuno LS4100 ??any good ??
Yep, the big knobs on the sides hold it in its bracket. I don't leave anything on the boat either. Way to much money invested to offer them up to any petty thief spry enough to jump up into the boat.<br /><br />Let me talk about range scales for a moment, because they are generally not understood at all and they are really important to getting the very most out of your fish finder.<br /><br />The first thing you have to understand is that there are a couple of performance characteristics of your fishfinder/transducer combination that are variable. The two most important of these are the pulse repitition rate and the pulse duration. That is to say the 'ping' rate and how long every ping lasts. <br /><br />In shallower water the rate at which the fish finder (when I say that I mean the combination of display unit and transducer) pings can be very very fast, often at a rate greater than 1,000 per minutes (I think a LS4100 will ping up to 1,500 per minute). It can get away with this because in shallow water it doesn't take very long for the sound wave to leave the transducer, hit bottom, and bounce back up. So because it doesn't take long you can pack a lot of pings into a short period of time. At the same time in shallow water the ping duration has to be very short in order to allow a lot of them to be emitted. That is pretty straight forward.<br /><br />This is very good because the more pings you have the greater sample the fish finder can draw from to decide what to display on the screen. Now I know that is personifying a mechanical device, but cut me some slack here because I'm trying to explain this with the expectation that there are some people reading who know very little about how this works. Anyway, it is desirable to have as many pings as possible going out, but there are limitations.<br /><br />The problem is that when you get into deeper water you need to have a fish finder that pings at a slower rate. It simply takes time for the sound wave to make its journey down and back and the deeper the water the longer it takes. A transducer can not be making an outgoing sound and listening for a returning echo at the same tme so the ping rate has to slow down just so time is available for listening.<br /><br />When a fish finder is required to operate in deeper water it needs to shoot slower, that shold be pretty obvious. The thing is that it costs money to build a fish finder with the capability of a wide range of ping rates or pulse durations. Still, its a needed function for the fish finder to operate across a wide spectrum of depth.<br /><br />So, a way that fish finder makes approach the problem of pulse rates and durations is to divide the possible depths their machine might operate in into ranges. By that I mean that they might establish a range that covers the water column from 0 feet to 30 feet and call that range one. When the fish finder is operating in range one it will shoot at its fastest rate and the pings will be of their shortest duration. Then the maker might define a second range from 31 feet to 200 feet, and use a slower ping rate and longer pings when operating in that range. Finally they might set a third range that was 201 feet to infinity, and when set in that range it would shoot at its slowest rate and have the longest pings.<br /><br />Keep in mind that it is desirable to shoot at the fastest possible rate (with the duration really being driven by the ping rate) to get the most clairity out of your machine but that the depth of the water limits what can and can't be done in terms of speed. <br /><br />So with that as background it might jump out at you that when setting ranges the fish finder maker is stuck with having to live with the requirements of the deep end of the range but apply them to shallower water. What I mean by that is that in the example of 31 feet to 200 feet the machine has no choice but to act like its in 200 feet even though it might only be in 40 feet, which means that the quality of the picture you see when in 40 feet of water simply will not be as good as it could be because the machine is set up to operate as if it were in wate 5 times that deep.<br /><br />OK, with that said it should be pretty clear that more range scales is better. That is point 1.<br /><br />Now onto point 2. <br /><br />Most fish finders have an automatic function in which the fish finder will continue to follow the bottom as you move into progressively deeper water. As you go into deeper water from time to time the machine will jump to its next range scale and when it does the screen will be redrawn to encompass a deeper water column. It might go from having the screen show a maximum depth of 40 feet to a maximum of 100 feet or 250 feet or something like that. Of course as the screen covers a larger column of the water the detail it is able to display decreases. That means that given a choice it is always to your advantage to show as little of the water column on the screen as is necessary to cover the bottom or whatever other display that might be of interest to you. So you need to keep that in mind too. Now, there is another thing, when a fish finder shifts from one range to another it takes it a little bit of time to decide if it is operating in the right range. What the machne's internal logic will do is compare the strength of its strongest return echo with the depth range its set to. If it finds itself receiving echos that are illogically strong it will automatically switch to a lower range scale where stronger returns are expected. The opposite is true too of course. <br /><br />Now this really wouldn't matter very much except for one thing, if you are moving from deeper water into shallower water what you will be left with is a blank screen while the logic circuitry is doing its thing and that may be a blank screen while you are screaming hell-bent for a grounding. It is very undesirable to have a depth finder switch range scales while you are running in shallow water.<br /><br />So, that's the background, in simple terms. In the real world it works out like this. If you can buy a machine which allows you to define your own range scales you will be better off than having a machine where they are factory set and locked. As far as the ping rate and duration go you can't do anything about them (before you guys with new Lowrance machines start screaming I'll address their variable ping rate feature in a minute) because they are locked by the properties of sound in water. <br /><br />Basically what you want to do, if your machine permits it (and all Furunos do) is to set at least one range scale so that you can use it while running in the shallowest water you normally encounter without it flipping scales on you while you are running (which, as you now know blanks out the screen). Say you run out through a creek that has a minimum depth of 4 feet and a maximum depth of 12 feet. I'd set the first range scale to something like 15 feet just so as long as I was running it would always show me bottom and not blank out at any time. If I then move out into open water where I fish pretty often and its something like 30~40 feet deep I would want my second depth rante set to something like 45~50 feet because it will allow as much of the screen as reasonable to be used and once again, it would not blank out while I was most in need of it. This would continue until all the ranges had been set.<br /><br />Now, the next thing. Remember that the repitition rate (PRR)is fixed and is a function of range but if you are able to change the range scales it doesn't change the fact that the rate is fixed. So one of the things you need to keep in mind when setting ranges is that you want to, if possible, stay right at the upper end of the PRR. Normally you can figure out where that is pretty easily. The screen advance rate, how fast the picture marches across the screen, is linked to the repititon rate. You can over ride the advance rate on Furuno machines (and quite a few others too) but in truth it doesn't give you any more information or improve clairity at all - its an illusion but one that traps a lot of guys.<br /><br />Oh, I almost forgot to say something about that variable pulse rate that some of the new Lowrance machines are selling as a special feature. It is not anything special at all, its just marketing hype. What Lowrance has done is purposefully slowed down the pulse rate (remember, you can slow it down all your want, the limitation is on how fast it can ping, not how slow) by 50% and then they give you the ability to bring it back up to where it should have been in the first place - which happens to be exactly where every other fish finder made, including all the other models by Lowrance, is operating anyway.<br /><br />There, did that help any?<br /><br />Thom
<br />Good Fishin to you.<br /> Phil
