Bow chain

I bought a used fiber glass lund.

there is not a bow chain.

Is it needed on a bunk trailer?

If needed, does it attach to loop on main beam down below? Seems odd.

Yeah the safety chain on your winch is just as important as the safety chains on your trailer. I wouldn’t tow without it. 

In my opinion, you need one. If it isn't required by DOT, it should be! All you need is a 12-16" piece of welded chain, two quick links and a hook for the bow eye. If you're worried about the chain hitting your boat (it shouldn't, but you never know) or trailer, then get a piece of vinyl tubing and put the chain through it. I've had a winch strap break and also had the lever that keeps the winch from unwinding fail, both of which the safety chain saved my boat (and I, too, have a bunk trailer). I also replace my winch strap every 3 years, whether is shows wear or not. They are $15...a heckuva lot cheaper than an insurance claim and time on the water missed! A DIY safety chain will run you about $8-10 at most hardware stores. Why wouldn't you do it? That's my $.02

my FH1750 trailer didn't have a safety chain, went to the local True Value hardware and they helped make one out of cable, worked great!... we picked out the raw materials, and they assembled

The Ranger I bought last year same thing , strap no chain, first thing I bought was a chain and installed it . I had a winch go bad on my last boat and it was a bunk trailer just like what I have now , was cruising home noticed something didn't look right after a few miles of bumps , sure enough the winch loosened up and the bow safety chain was the only thing besides the rear straps holding the boat on the trailer.  I won't own a boat and trailer without one on it from here on out .

yes, it attaches to the loop below. I have always had bunk trailers and  wouldn't be without one...it isn't only for loading/unloading, if the strap breaks there is nothing holding down the bow of the boat if a big gust of wind hits it...IMHO of course