Single axle ALI I beam with skids would be my pick.

My last boat weighed 2.8T and it was no dramas winching it on to skids  with no rollers at all. I always wet the skids which I'm not sure if it made any difference. Only time it was hard work was if the ramp was really steep

Hi gilly my 2 cents

after having a wheel come off @100kmh from loose wheel nuts on a single axle trailer, I would seriously consider the twin axle

skids you need to go in deeper but need little maintenance, those Teflon strips last a long time. If your considering beach launching much rollers are better for shallow launch retrieve

 I have had both under my Cruisecraft, the skids last forever and you can wax them or spray with silicon spray.
I have rollers under it now though

Dual axle pretty much every time unless maybe you just go around the corner to launch-always

I have also had a blowout on my old dual axle Trailcraft trailer near Billabong at 100kph, no swaying just saw rubber flying out.
Single axle would have been a different story I reckon.

 I have both under my 7m ally. Full rollers with v skids to guide it on. Works as a proper drive on trailer from any angle. Makes a big difference when retrieving solo or with a good cross wind. 

 I have full skids. Ally boat. 3500kgs all up

Hate rollers. Hate carpet bunks

If you did a lot of beach launching i might opt for keel rollers.

As rob said you can always lube them up i havnt needed to. Boats on the trailer in 12 seconds with the leccy winch!

Dual axle everyday of the week. Only downside is extra maintenance in my opinion. 

 Should last forever as you can always redip if necessary. On the subject of single vs tandem, I've done both and tandem tows better--like Rob, I lost a complete wheel once and all I felt was a bit of a tug--slowed down and the wheel rolled off and into the scrub on the Exmouth road. No drama to fix there and then if carrying a spare hub. Blowouts, the same. Single easier to manoeovre around on the jockey wheel by hand. If you go tandem, IMO, don't go for single slipper springs, go the full load sharing assembly.

The keels on ally boats will eventually chew out the hard blue rollers, but they'll last longer than the red ones and much longer than rubber--rubber is meant for fibreglass. My last 6m tinny had rollered keel and side bunks of that blue material, I just found it easier to have someone holding the rope then jab the brakes  in reverse to slide it off. My new trailer has rollered keel, with a couple of roller bunks up front and  carpeted bunks right at the back, certainly launches easily on a flat ramp.

 Is what I have on my 6.8 seaquest.....self centres, no roller maintenance and slides off with ease, would never have a rollered trailer again !

 The only thing I'd have to say Gilly is lighter towing with single axle, easier maneuvrability on the beach. And as other have said rollers for an easier launch. Structural wise I'd be going for uni beam type section, tube and channel easier to work with build wise but both have their downfalls. 

gilly ,

I do 50/50 of beach and ramp launches , so I use rollers, find them easier trick is to keep them well lubed

trailer imo , would be a tandem every time , as with rob and ranmar , have had blowouts and whole wheel hubs come off , with a tandem its less hassle min damage done and if you absolutely must I have towed slowly on 3 wheels to get to help or home ,

rocker springs on the tandem work better then slipper , tandems are easier to tow and reverse ,they carry the weight much smoother imo ,

hezzy

 cheers for your thoughts so far. 

 im certain this trailer is fixable and the rollers are an easy fix but at 18 years of age im tossing up whether it is worth throwing another couple grand at.

 i did have a quick look at a C channel trailer today and came away dissapointed from both quality and sales staff. 

 i guess cash doesnt talk anymore 

 probably need to hatch a plan andy and "rebuild" my trailer

One thing you need to consider is the actual boat.

Alot of the ally boats are not designed to sit on a fully rollered or skid(some types) trailer.

Many need to have a significant amount of the weight taken on the keel and just use the rollers etc for balance.

If you have too much weight on the rollers they can cause the hull sheets to bow into the hull which can affect the boat when underway or even cause cracking.

 pressed ali does not do well if you have rollers on the bunks and the weight is concentrated in small spots rather than over the larger area of a skid bunk. If the rollers are between frames they will push the sheet in and can cause cracks. That said, the bunks should be there to stabilise side to side movement, not support disproportionate wieight--the weight is meant to go on the keel, IMO.  Plate hulls are usually OK with roller bunks?