Trailer Tongue Weight

[jfrench]

Found this interesting bit of info about boat trailer tongue weight on the ShorLand'r web site:

To determine proper tongue weight, total the package weight (boat with fuel/battery, motor with maximum horsepower, and trailer) and multiply it by 6% on single axles and 5% on tandem axle trailers. ShoreLand'r suggests that tongue weight may be acceptable in a 5-7% range.

http://www.shorelandr.com/pages/pf_trstep3.htm


Regarding some recommendations at this forum to set tongue weight at 10%, I saw that number used on another site regarding travel trailers.


By the way, the reason I was looking at this information is because as I was working on painting my trailer yesterday, I noticed that the boat is positioned well to the rear of the trailer frame. It hangs off the back four or five feet, and there is about that much extra space at the front. The wheels and axle are also well to the rear of the frame. When I unhooked the bow cable, I could rock the boat on the trailer with one hand. I'm thinking I should move it forward on the trailer, then move the trailer wheels and axle forward to retain the same tongue weight. Does anyone know how our boats should be positioned relative to the trailer frame?

 

[Ken]

A hard call, since there are so many different trailer types used.
Like you I've heard 10% all my life...

Does your trailer have the movable axle carriage?

Looks like your going to have to find a scale though...

On the single axle swing keel trailers, it always appeared to me that the center of the axle is just to the aft of the center of the back window. Not very scientific but close enough for a good starting point for you.

 

[watercolors II]

Closer to 10 percent.

Having a 1987 model like yours and not knowing the total weight of boat, gear and trailer using a 3500 lb starting point I come up with 175 lbs at 5 percent and 245 lbs at 7 percent.

In real life, I changed tow vehicles a couple years ago and because the new vehicle was a conversion van I didn’t want to back it as deep into the water as the former pickup. I extended the tongue 18 inches without moving the boat or it’s location over the single axle trailer. Using a bathroom scale the tongue weight changed from 311 lbs. to 282 lbs. and the unit didn’t tow as well.

What 30 lbs of unweighting of the tongue didn’t cause the trailer to sway but, put a bounce into a 6200 lb vehicle with fairly new shocks. Moving the axle back 1.5 inches restored the original tongue weight and made life livable again.

I believe closer to 10 percent would work much better.

Now, for your rocking situation, as you say your boat may not be balanced on the bunks or the bunk supports may be weak. I think the universal laws on overhang beyond the taillights maybe 4 feet without attaching a flag.

My unit has worked very well over the last 20 years, photo attached, pictures are worth 1000 words.

 

[Chris Patterson]

Hmmm, I would think.......if the bow cable pulls down on the boat at all, it will change the weight differential on the tongue. Or down for that matter. Even straight in to the bow support rubber on the trailer will make a difference, as you've now put weight farther forward. Interesting thought..

i'm almost sure of it....

 

[jfrench]

Well, I must be OK. My axle is positioned about the same as "Watercolors," relative to the rear window; and my boat's sticking out about the same amount to the rear. The difference is in the overall length of the trailer, mine is longer out the front. The rocking I reported earlier seems to actually be the trailer frame flexing! If it hadn't been towing this boat for 26 years I'd be worried. I think adding a bow roller to support the front would be a good idea, I don't have one now.

 

[watercolors II]

Bow roller

I don’t think using the boat as an object to add support to the trailer is a good idea. If your trailer is flexing, try not to tie the boat to that part of the trailer real tight, the part that’s not moving is where you want the boat strapped.

A bow roller is a great aid in helping recover your boat if it’s placed in the right position but, with the hull in it’s final resting position keep clearance between the hull and this roller, at least 3/4 inch.

If the hull is strapped tight to the bunks then this roller is going to add real stress to that small part of hull where the roller makes contact when that part of the trailer flexes up, if the bow is tied down tight the same thing is going to happen.

Your boat is totally supported by the bunks, your winch keeps the hull from walking backwards on the bunks due to road vibration. You need the winch to place the hull in the exact spot on the trailer every time or you throw the towing balance out, not really to support the bow weight.

 

[jfrench]

OK, I won't add a keel roller.

What about supporting the swing keel? Right now mine is only supported by a single rubber roller located about 2/3 of the way back from the pivot pin. I've seen some trailers with a flat bunk board under the keel and have heard on this forum that it's better to support the keel only near the rear like mine. That way bumps in the road are absorbed by the keel swinging rather than being transferred directly into the pivot pin. Any opinions about proper swing keel support?

 

[txtowman]

I think all the advice is spot on in this thread.

My trailer flexes way more than I would like.

The more tongue weight you have the better your trailer will pull, this is also dependant on your tow vehicle, I have only towed mine with a dually and if the tongue is light I can really tell. It feels like driving head on into waves if it is light.
I can lift 200 pounds and can't budge the tongue.

I agree with the bow roller gap, mine loads way better with a roller, without it the boat ends up 6 inches behind the bow roller no matter how tight the winch cable is.

No worries with the overhang, that 4 foot law is for hauling freight not for a dedicated trailer that would likely drag the ground going through dips and over humps.

I hope to have my trailer design perfected by the end of this summer, and I will build a new trailer from scratch.

Your keel support is just right, it needs to support the rear to keep pressure off of the keel lifting hardware, and the bridge deck.

This is just My opinion, I have moved My boat all over the trailer to get it to pull and launch well.

 

[watercolors II]

With a full keel support you would be walking a fine line between the support carrying the weight of the keel and the tolerance to close at the front that some of the weight of the hull would be sitting on the keel pin and bolts.

With just the back of the keel supported you would be removing almost half the weight of the keel on the pin and bolts which would be much less stress in this area than when the boat is moored all the time.

Don’t discount the value of a bow roller for recovering the boat. I said make sure the roller is not in contact with the hull when the boat is on the trailer, what happens when the trailer is in the water on the angled launch ramp this roller becomes higher than the floating hull because the boat is level on the water. Placement becomes critical in that there’s two places to put it depending on the angle of the launch ramp.

If the ramp is not of a great angle then the roller can be placed about 2/3 of the way back from the bow to the front of the bunks. With the trailer angled down the ramp this roller will be higher in relationship to the end of the bunks than when on level ground. As the level floating hull makes contact with the upward projecting ends of the bunks the bow starts to ride higher out of the water as it rolls on this roller thus eliminating some of the friction caused by the ends of the bunks.

If the ramp is very steep, like some of those on the Chesapeake, then the roller can become a stop to keep the bow from running in under the winching system. This roller would be very close to the front of the bow and would be very much higher out of the water on the ramp than the previous location mentioned. This would stop the hull from going forward, the bow would hit the side of this roller and then the winch would start to lift the bow up the front of this roller till you start to reach the transition from the vertical part of the bow to the horizontal part of the bottom, at this point the roller would then start to carry some of the weight of the hull and relieve the stress on the winch and boweye.

When the stern settles down on the back of the bunks as you come up the ramp, the bow lifts a little allowing for this gap between the rollers in both locations.