CONTINUOUSWAVE

I am currently having a trailer built for a 1986 Frontier 25. It'll be a tandem axle with each axle over-rated for load.

With regard to the center of gravity of the boat with engines and full fuel: at what hull station is the approximate center of gravity?

This is needed to get proper tongue loading but not have more load on either the front or rear tires.

Contacting Brunswick didn't yield any results.

It will also be useful for you to know the approximate center of gravity (CoG) of your new trailer. The tongue length, coupler, winch stand, winch and strap will cause the CoG to be further forward than might seem logical. Your engine choice and fuel tank capacity will also play into the CoG location.

I believe that for most single axle trailers carrying Boston Whaler boats the axle is located below the console suggesting the CoG is in approximately that location.

When we had a custom trailer built for a Boston Whaler the fabricator required the boat be located at his facility for measuring purposes. I believe the boat was fitted to the trailer before the axle was installed. That would have made determining the boat and trailer CoG fairly simple.

A two speed winch makes loading a 25 foot boat onto a trailer much less work. Dutton Lainsing makes a good two speed winch.

I do not have any information about where the center of gravity of the hull of ANY Boston Whaler boat will be located when the boat has engines and a full fuel tank. Also, I do not have any hull profile drawings of ANY Boston Whaler boats with the traditional "hull station" locations specified.

Trailers with tandem-axles sometimes have the axle springs arranged in a manner than tends to equalize the weight load on the axles.

I don't know of any reasonably accessible method to measure the individual axle loads for a trailer with dual axles. Most truck scales are designed to measure the total load of a set of axles on the trailer, and they won't be able to give you a measurement of load on an individual axle. About the only inference regarding weight load for tandem axle trailers might be to carefully monitor tire temperature.

Tongue weight is determined by the position of the axles on the trailer AND by the position of the boat on the trailer. Adjusting the position of the axles on the trailer--if that is possible, that is, if the axles are not constrained in a location by welded attachment to the frame--can be done to affect radical change in the tongue weight. Movement of the boat relative to the trailer is often sufficient to cause a significant change in tongue weight. Movement of the boat is usually accomplished by movement of the winch post, which, again, if not welded in place, ought to be relatively more easy to move and adjust than moving the axles.

In general an outboard engine boat with an integral fuel tank will have most of the total weight in the aft half of the hull, so the trailer axles would certainly be located on the trailer with that in mind. I don't know that a 1986 FRONTIER 25 boat would be unusual in regard to location of center of gravity compared to other 25-foot outboard engines boats of similar layout. On that basis I would expect the trailer manufacturer would have experience with other boat that could be useful in estimating the weight distribution on your boat.

Because a FRONTIER model was made by Boston Whaler Commercial and Government Products (CGP), you may be able to get information from them. They used to be a part of Boston Whaler but are now a separate division of Brunswick. If your mention of "Brunswick" as a source that yielded no information in your initial post was in reference to the new division, perhaps you could get some information from Boston Whaler customer service, as they may have some old data available.

Also, there are many images posted on line that show a FRONTIER 25 boat on a trailer, including some with tandem-axles. You could infer from those images the approximate location of the trailer axles. You can find these images with a search term:

https://www.google.com/search?q=boston+ ... 5+for+sale

I would think you would have your trailer built like a normal tandem axle trailer and have some length on the tongue to allow the front post to be moved forward or back to shift the boat forward and backwards to set the tongue weight appropriately . You want the tongue to be 9 to 15% of the the total weight. Setting this trailer up should be the job of the trailer manufacture when they custom make the trailer for your boat and they should be setting this up for you. SO the tongue of a 5000 lb trailer should be about 500 lb. Center of gravity is not needed to set this up, just the ability of the trailer to allow the boat to be moved forward or backward to get that tongue weight correct. Setting the axles where they should be should be done by the trailer builder. Have them move the axles if they are off. Moving the axles on a trailer like this is a chore if not impossible once the trailer is made and brake lines set and things are all welded up.

Since you are having the trailer made I would assume you have a ballpark of what your boat weighs already. There are many ways to get this weighed.

At weigh station weight the trailer alone while attached to the truck but the truck not on the scales, just the dual axles of the trialer. Then weigh the trailer unattached to the truck with whole trailer on the scales. This will give you the total weight and then subtract the first weight with the truck still attach and you have your tongue weight.

Or put the tongue on some heavy weight scales. Going over weight will mess you tow trucks stability up. Going under weight will guarantee massive sway and you will end up in the ditch and on youtube. you probably know all of this but it still happens to people.

The notion that a boat trailer must have "9 to 15%" of total weight as tongue weight is not supported by my experience.

A big boat like a FRONTIER 25 and an appropriate tandem-axle trailer will probably have a total weight of more than 7,000-lbs. If the tongue weight were 15-percent of that, you'd have over 1,000-lbs of tongue weight. There is hardly a hitch coupler, a hitch ball, a hitch, and a tow bar on a truck that will tolerate that kind of weight. A further problem: where would you get a tongue weight scale that goes to over 1,000-lbs?

A very serious problem with excessive tongue weight is the reduction of weight on the towing vehicle front axle. Less front axle weight leads to poor steering and the potential for the front wheel brakes to lock up under hard braking. If you drop 1,000-lbs on the hitch of any truck, the front axle weight is going to be affected.

I have not checked the tongue weight recently on my trailer, but last time (c.2008) I made careful weighing of the rig the weights were:

BOAT + TRAILER = 5,600-lbs
TONGUE WEIGHT = 460-lbs

That is 8-percent tongue weight. I think since then I moved the boat back an inch or two on the trailer, and the tongue weight is probably lighter. That boat and trailer have been towed extensively on the highway, probably more than 25,000 miles, and there have been no problems related to insufficient tongue weight.

I think the general advice to have tongue weight at 10-percent or more is from people towing travel trailers. Travel trailers have much more wind area, have a much higher center of gravity than boats, and often are on trailers with very long overhangs beyond the rear trailer axle. Boat and boat trailers tend to have less wind era, a lower center of gravity, and usually have the trailer axles offset to the stern of the boat, reducing overhang beyond the rear axle.

There is a very thorough discussion of how to calculate hitch load change with axle movement in a article in REFERENCE. See

http://continuouswave.com/whaler/refere ... tions.html

There is even a DOS executable program to perform the calculations for you.

Thanks all for the replies. The trailer is being built in the lower 48 and the boat is currently in Anchorage AK area. The trailer it was on is undersized and the rear tires showed overloading and abnormal wear from the trek north. I like the idea of having the boat movable fore and aft to get a proper tongue weight.

Tow truck is a Dodge 2500 Diesel and should support 1000 lb tongue weight but 500-700 lbs would be better. Tow capacity is 16K lbs. Looking online at other Frontiers shows a pretty wide spread of approximate axle locations.

Where the trailer is being made off-site having the boat adjustable fore and aft might be the best way to achieve this.

I like to be able to lift my trailers tongues to make slight adjustments to the position relative to the ball when hitching the trailer. The galvanized steel trailer under our 190 Montauk is too heavy for me to manage that so I like to have a guide when hitching that trailer. Otherwise I find myself making numerous trips between the drivers seat and the trailer hitch in order to get the job done. The aluminum trailer under our Sport 13 is much easier as I can lift it's tongue.

I would like to try adjusting the Montauk farther aft on the trailer until I can lift the tongue and then test the arrangement for driveability. I suspect it will tow about as well with fifty or so pounds of tongue weight as with 200 pounds.

I expect most folks are able to lift a great deal more weight than fifty pounds but as I approach my 80th birthday that's about my limit. At this time in my life I have to find ways to get things done that don't require me to work as hard as I used to.