I didn't say that. I said just the opposite - that he will be fine with the connectors and RG58 he is planning.
The loss difference over 12' of RG58 pigtails compared to 12' of RG8X pigtails is 0.07db. There will be no practical or measurable difference between them.
The OP stated his desire for doing this was to put the splitter in a better position. That implies that using smaller, more flexible coax will be helpful, as well as the splitter will be in a better environment. If this is true, then those reasons are far more important to ruggedness and operation than preserving 0.07db.
While connectors add a theoretical potential loss, they do not add a measurable or actual one, unless they have been done incorrectly, or poor quality connectors have been used. It is pretty much an old wive's tale. There is a guy on here who posts infrequently, but always about radio topics, who is a professional in this area with lots of measurement equipment. As an experiment, he put together a long string of a dog's breakfast of connectors - including BNC and other seemingly inappropriate ones - and could measure no meaningful loss through them. So adding a couple of good quality, well-made connectors in a system for pure convenience sake is just fine.
I would consider it preferable to running a single piece of coax from the mast top throughout the whole boat. Pulling all that, and putting it back in, every time the mast is pulled would be a pain. Also preferable to having a piece of equipment located in a poorer or less convenient environment just for the sake of not using connectors.
But even if the OP just wanted to use 12' of RG58 and multiple connectors only for the pure fun of it, he will be fine.
My comment was on your suggestion to use LMF 400, sorry for the confusion and my lack of clarification, it was late and an edit. again sorry should have reread what I was stating.
I will agree to disagree with your statements on connectors and the numbers however, as my knowledge is first hand and yours appears to be second hand, but I will agree that at 100 to 200 Mhz there is probably no discernible difference, measurable...depends on your test equipment.
To state that a BNC is inappropriate connect is also a misnomer, as it is good for general use up to 2 Ghz so for VHF and AIS they are perfectly fine. In fact BNC and TNC only differ in that BNC is Bayoneted and TNC is threaded, they are both NC connectors.
Also stating that the difference between RG-58 and RG-8X at 12 feet being 0.07 dB is only true for the manufacturer you choose, as RG-58 and RG-8X are sizes and do not necessarily impart a standard of lose, in fact they are not standards at all they are simply sizes as previously stated. What does this mean in the big picture of things is that the losses per 100 feet at a given frequency vary from manufacturer to manufacturer, even between Model/Type within a manufacturer take Belden 8240 and Belden 9201 both are RG-58 using the 12 foot length previously stated and at 161 Mhz at 12.5 watts to simulate AIS transmission, the 8240 has 0.593 dB of loss, to put this into wattage the output at the other end of the 12 foot cable would be at 10.904 watts. For the 9201 the results are 0.64 dB of loss and an output power of 10.787 watts. Same size cable same length but 0.117 watts difference. Why is this important 2 fold all losses are additive, duh and these are the losses over only 12 feet of cable as the length increases the difference in loss will to as it is a function of distance.
My point is not all coax cable manufacturers build to the same specification there are good, Times Microwave Systems, and bad Chinese won hung low brand. One cannot say that all RG-58 has exactly x loss difference compared to all RG-8X, one has to know the manufacturer and the model/type of the the RG-58 and RG-8X, then and only then can one say that the loses at x feet is x dB for these two specific cables.
BTW I used the following web site for the calculations Coax Loss Calculator
I also used a perfect 1:1 VSWR as to only compare "ideal cables"
What can be said that in general one will have less losses using RG-8X as apposed to RG-58, and if tight corners are an issue why not use 90 degree connectors, it is what they where designed for.
colemj you are correct in a perfect world a single cable from antenna to radio is best, being that we live in the the real world that next best option is to limit the number of connections, this limits the number of potential failure points/ water intrusion/ points for corrosion. So in general keep the number of coax cable to the absolute minimum.