Bunk vs transom relationship

[jimmbo]

Another pic of mine, taken immediately before the one above, it shows both the chine and outer strake both out of the water at the transom

Where on the hull do the bunks make contact? From the keel to the strake, the hull should be straight, and the bunks should go to the transom. If the bunks are located between the strake and the chine, the trailer is not set up correctly. If you have 2(your case 3) sets of bunks, the ones between the keel and chine should go to the transom, then the outer ones can, and should be forward of the hook

A photo of the transom area of you boat/trailer in question would help a lot

 

[DouglasW]

First, I do not have an issue with your explanation of the purpose. That makes perfect sense.

On my boat, which is similar (but not exactly the same) to the one in the photo, there are "hooks" at the chine and also at the first strake inboard from the chine. All three bunks on each side go only as far aft as the start of the "hooks" and they cover almost the entire surface between the strakes and the chine. They are flat, not upright/on-edge and are supported at several places. The trailer was custom designed by the boat's manufacturer to fit this specific boat, so I would assume they knew where to best locate the 6 bunks. There are no adjustments possible on the trailer. As far as I can see, the only bunk that could be extended rearward would be the inboard one on each side, but then there would not be good support for them to the trailer. Unfortunately I do not have a good photo of the boat on the trailer as seen from the back. The boat stays on the lift until there is a hurricane and it has to be moved. I can take some then if needed ;-)

p.s. Your Glastron rides a lot higher at speed than my boat does, at least as far as I can tell. Must be over 300 hp?

 

[harringtondav]

Interesting discussion here. Based on some tech manual that I can't find right now, hooks and rockers are to be avoided. But hull design is advancing. But I still believe supporting the transom during trailering is prudent. So I edit my reply above to still get the bunks under the transom. But if your boat is designed with a hook, consider the adding shims to the top of the bunks to support the concave/high surface of your hull. A good location would be under your front engine mounts. This and transom support would fully support your engine/drive, and isolate you hull and stringers from bending and bouncing.

 

[DouglasW]

I will assume that my trailer design is correct as is, since it has been in use since 1999 and has made at least one cross-country trip from Idaho to Jacksonville (FL) without any cracks, sags or other abnormalities. I suggest asking the manufacturer about this.

 

[boatman37]

Looked at mine today and the rear crossmember is about 16" or so in front of the transom on mine but the bunks extend about 12" or so past the last crossmember. But yes they are doubled up on edge so should be very strong. Just need to figure out the best way to get the bunks further back.

 

[jimmbo]

This is going to sound like I'm flip flopping, or back pedaling, but it is not. On an Outboard Boat, in most cases, the most weight is on, or aft of the transom. So the transom needs to be supported. On Inboards and I/O, the weight of the engine(s) is further forward, so maybe in some cases, and if the area under the engines is solid enough, and the trailer bunks are located there, it may not matter if the bunks don't go all the way back. If the Boat manufacturer designed the trailer for the hull and vice versa you should be fine.

 

[boatman37]

I was wondering the same thing Jimmbo. Most of the weight is probably 2-3 feet in front of the transom. I still think it would be best to go all the way back with the bunks but not sure it would hurt if it didn't?

 

[boatman37]

I just emailed Crownline to see what they say. I will let you know.

 

[boatman37]

Well they sent me a drawing and a data sheet with all measurements. They didn't directly answer my question but the trailer spec sheet shows a measurement going all the way to the end of the transom so guessing that is what they recommend.

 

[harringtondav]

On Inboards and I/O, the weight of the engine(s) is further forward,.

In a stern drive the engine's weight is shared by the front mounts and the rear mounts which load the transom. The front mounts are set rearward on the engine, so support more weight than the transom plate. But add the weight of the transom assembly, plus the out drive's weight and it is still a hefty load. I'm no marine engineer, but I think their focus is structure stability and performance on the water. So I believe supporting the transom on a lift or a bouncy trailer is important.

I have a Shorelandr "EquiLoad" flat bunk trailer. The rear half of the flat bunks have two supports each on a teeter-totter beam. This lets the bunks conform to the heaviest area of my boat. The front bow supports just ride along.

 

[DouglasW]

I just emailed Crownline to see what they say. I will let you know.

Crownline? From you first post, I assumed your boat was a Searay. If the bottom is flat at the stern and strakes, I see no reason to not have the bunks go all the way back. Some manufacturers avoid that because it can interfere with transducers and the like, but if there is no conflict, no problem.

 

[boatman37]

Crownline? From you first post, I assumed your boat was a Searay. If the bottom is flat at the stern and strakes, I see no reason to not have the bunks go all the way back. Some manufacturers avoid that because it can interfere with transducers and the like, but if there is no conflict, no problem.

Yeah. Had a SR before the Crownline but still visit their forums. When we had the SR the one season we pulled it and 2 dock neighbors helped get it on the trailer and had me pull it up too far and broke the depth finder transducer...lol. The CL has nothing hanging off the back other than outdrive and trim tabs

 

[boatman37]

So this summer I moved my winch post and bunks forward about 10-12" cause I knew the tongue weight was light. So pulled the boat Friday and today took it to the scales. Truck is a 2018 2500 Ram 6.4 Hemi outdoorsman off-road package crew cab 4x4. Truck with me in it and 1/2 tank of fuel was 7240. Boat is a 2006 Crownline 250CR with A/C. Dry weight is listed at 6600lbs. Trailer is a 2016 Venture aluminum tandem axle weighing 1325lbs (according to Venture). So boat had about 20 gallons of fuel in it, 7-10 gallons of fresh water and black water was empty. Everything else was as we use it with anchor, life jackets, etc. Total weight was 15,900lbs. Truck with trailer connected but only weighing truck axles was 7920 so 680lbs tongue weight. Works out to 7.9% tongue weight. If I had a full tank of fuel that would add 300lbs and maybe 100 extra on the tongue. That would put tongue weight at about 9%.

So boat itself was 7335 (dry weight listed as 6600).

Here are before and after pics. The before was with the boat back about 12" further. The after was after I moved the winch post and bunk boards and is the way it sat today on the scales.

Forgot to add, I'm looking at buying a different insert rated at 15,000lbs and my trailer sits slightly higher in the front so if I get a little more drop that will add a little tongue weight too.

with truck (before also):

AFTER: