HELP! Bobbin thread on top only when start sewing

[Quade]

I'm not sure if it's just the angle of the picture but the hook looks mighty blunt and even beat up in the top two pics.  If it was my machine, I'd probably replace that hook.  Not that that's necessarily related to your problem.  

Have you tried different bobbin holders on the two machines?  One thing I like about the 1541 style is the easily replaceable bobbin holders. Whereas on the vertical hooks,  the bobbin tension spring is built into the hook. The downside is you can't easily see remaining bobbin thread on the 1541. 

I think the gap between the hook and the needle is too wide on the 1341.   Notice the gap on the 1541.  I almost wonder if the 1541 is too close so it's been hitting the needle and that's why the hook has gotten blunted. 

 

[Gump]

 

In your first pic you show, the thread is the same diameter as the threads of the material, so you can't hide a two thread knot in material only one thread thick. I have had similar problems when sewing Sunbrella fabric with 92 thread. On a single layer the knot would be on one side or the other. A larger needle does help, but on long runs it will tend to shrink your fabric, [lost 1.5" on a 60" run]. Depending on strength requirements, you could use 46 with a size 16 needle and more stitches per inch. I gave up doing boat tops because their not fun and leather still is !