How to Measure to Fit a Boat Trailer

How to measure for the correct trailer

Our trailer listings include three specifications. "Bow Eye to Transom Minimum", "Bow Eye to Transom Maximum", and Boat Hull Size Minimum and Maximum. The information provided below should help you better approximate how your boat will sit on a trailer.

The diagrams display the correlation between the boat hull and trailer dimensions.

If you would like to look up boat's dimensions or weight click here.

The Bow Eye to Transom measurement as shown in the accompanying diagrams is the most critical in sizing a trailer for boat length. Pulpits and Euro transoms are generally not supported by the trailer. Including these in length measurements could result in a trailer that does not fit well however they still must be a consideration when choosing a boat trailer.

These trailer schematics are provided to illustrate the dimensions displayed on many of the product charts that follow. Most of our boat trailers have a great amount of adjustment in the support structure. Adjustment to either extreme may require moving the axles to maintain tongue weight in the 5% to 7% ideal range for most trailers.

Schematics are a visual representation of a generic trailer and not drawn to a particular scale.

If you have any question about which trailer is right for you please call us toll free at 888 278-1991, 8 am to 5 pm Monday - Saturday. You may also email pictures of your boat for the purpose of choosing a trailer to info@topnotchmarine.com.

"A" Bow Eye to Transom Maximum

"B" Bow Eye to Transom Minimum

"C" Rear to Angle Support

BUNK DIAGRAM

ROLLER DIAGRAM

BOAT DIAGRAM

OTHER IMPORTANT CONSIDERATIONS WHEN FITTING A BOAT TRAILER

Transducers:

If your boat has thru-hull or transom mount transducers you must be sure to position trailer bunks so they do not come into contact with transducers. In some rare cases, transducers must be moved to allow a boat trailer to fit properly if not the transducer and the trailer will likely be damaged.

Bow Pulpit:

A bow pulpit us usually a narrow platform that extends forward from the front of the boat. It can be functional or cosmetic. Pulpits usually provide support and extension to an anchor davit that supports the anchor on the end of the pulpit. When a boat has a pulpit, the way the hull is supported while the boat is loaded and unloaded is important. If a hull drops off the trailer while sliding in the water too early the pulpit may hit the winch stand. Bow guide boards are a common solution.

Motor Bracket:

Motor brackets are metal or fiberglass boxes that allow the mounting of outboard motors behind the boat’s transom. Brackets will increase the amount of weight on the rear of a trailer and are NOT counted when measuring the length of the hull. Axle position may have to be moved toward the rear to achieve correct tongue weight of 5% to 7% of the total boat’s weight.

Inboard Engine:

There are 2 types of inboard engine configurations that concern trailer fit. One is a straight shaft and the other is a V drive. The straight shaft places the engine more toward the front and the axle position on the trailer may have to be moved forward as well to achieve proper tongue weight. Secondly, additional clearance is needed for the shaft to clear the trailer frame. Most shaft drive boats up to 24 feet will fit on our standard aluminum trailers. A V drive is a consideration only in that the rear of the trailer needs to be strong enough to support the additional weight of the engine in the rear. The weight is similar to a stern drive engine configuration.

New Volvo Forward Facing Drive:

Your boat will require special fitting. Please contact us for more information at 888 278-1991.

Trim Tabs:

Trim tabs should not effect trailering in most cases. Always retract your tabs prior to loading your trailer.

TOW VEHICLE REQUIREMENTS

Please refer to tow vehicle capabilities supplied by the manufacturer and compare with trailer requirements.

Towing capacity: a tow vehicle must be rated for the full GVWR of the trailer being towed.
Hitch: a hitch assembly rated must be rated for the full GVWR of the trailer being towed.
Tow ball size: match tow ball to the coupler / actuator requirement (2” or 2-5/16”) depending upon trailer capacity.
Tow ball height: 18” to 21” from the ball centerline to the ground. Adjust by using an offset drawbar.
Trailer electrical connection: 4 or 5 pin flat pigtail connector if no brakes or surge brake equipped, and 7 pin round if Electric Over Hydraulic (EOH) brake equipped.

To calculate needed trailer capacity, calculate the total weight including the boat, the engine, a full fuel tank (approximately 7 lbs. per gallon), full water tanks (if applicable) and your personal gear. A good rule of thumb is to use 10% of boat, motor, and liquid weights for personal gear. Select a trailer with the next highest capacity rating. If you intend to carry additional gear or luggage in the boat over long distances, consider the weight of these items, too.

boat weight + engine weight + ((fuel capacity x 7 lb / gal)+
(water capacity x 8 lb / gal) = Total

Then multiply Total X 1.1

= Trailer Capacity Needed

Brake controller: required on models with electric or Electric Over Hydraulic (EOH) braking systems

TRAILER LOAD-CARRYING CAPACITY

To determine the load capacity requirement of your tow vehicle, refer to the Vehicle Identification Label attached to the trailer on the left frame rail just behind the tongue junction. It will display the maximum load-carrying capacity of the trailer. It is required to show the Gross Vehicle Weight Rating (GVWR) which is the load-carrying capacity plus the weight of the trailer itself. It is the trailer operator’s responsibility to ensure that the total weight of the boat, engine fuel, water, gear and trailer do not exceed the GVWR capacity.

If you don't know the correct weight of your boat and engine, don't guess; have it weighed. This usually can be done at a local lumber yard, feed and fertilizer store, quarry, truck weigh station, etc. Take the total weight of the rig and subtract the trailer dry weight that is noted on the VIN sticker.

Be especially careful not to overload the trailer by putting heavy items, camping gear, etc., in the boat while travelling. If you must carry such equipment in your boat while trailering, take this into consideration at the time of purchase and go to the next larger-size/capacity trailer.