Two Schools of Thought

How Ramp Design Affects Trailer Performance

When it comes to trailers for Boston Whaler boats, there is a big schism in the conventional wisdom. Some boat owners prefer a trailer with keel rollers that support the main weight of the boat and use small bunks only to provide stability, while another group uses trailers with full bunks and no rollers. Each group is certain they have the best approach. I have been studying this schism between the two schools of thought on trailers, and I believe I know what is behind it.

Trailer Designs

Styles of trailers are essentially divided into two camps: rollers or no roller. The roller group is further divided into to factions: keel rollers with bunks or floppy roller designs. As Boston Whaler boat owners we definitely do not want the all floppy roller type trailer, so we will omit this type from this discussion. We'll stick with a division between two styles of trailers: all bunk or keel roller with bunk.

The fundamental difference between these designs is that in an all bunk trailer there is nothing to reduce the friction of movement of the boat on the bunks. The weight of the boat bears on carpeted bunks and, lacking the lubrication of water and the upward force of buoyancy, movement of the boat fore and aft on the bunks is (in practice) impossible. Extreme forces would need to be applied to move the boat forward with the winch strap. Once the boat is hard on the bunks it is not moving anywhere.

In contrast, the keel roller trailer supports the majority of the boat weight on a series of rollers which, while far from frictionless, reduce the effort needed to move the boat forward or aft on the trailer to a small fraction of that of the bunk trailer. If placed on an incline the boat can be rolled off the trailer, especially when a small amount of upward force from a buoyant stern is added. Even when the boat is hard and dry on the rollers, it can still be moved by the winch strap.

For more information on trailer rigging, see the companion article to this one which concentrates on the proper trailer set up.

Power Loading

So that there is no confusion of terms, "power loading" refers to the practice of using the boat's own engine to propel it forward and upward onto the trailer, as opposed to manual loading by using a winch and cable to pull the boat forward and onto the trailer.

Influence of Ramp

The preference in trailer design is influenced by the type of ramps that will be used. There really are also two schools of thought on ramp facilities, so first I need to describe the two types of ramps. I'll call them the "Michigan" Ramp and the "Kentucky" Ramp, after locations where I have typically seen each type of ramp in use. And their design is really influenced by the water that they access. Once you understand the difference in ramp facilities, you will see certain types of trailers are more suitable for certain types of ramps, and this will be the underlying cause of the big schism in preferences for trailer designs. A review of these two types of trailer boat launching facilities follows.

The "Michigan" Ramp


The "Michigan" Ramp is a launch facility that has a ramp with a service dock that extends into the water right at the launch point. You launch or recover your boat alongside the dock. The dock is long enough so that when the boat comes off the trailer there is still room on the dock for the boat to lie alongside the dock.

Photo: Launch ramp with courtesy dock
A "Michigan" Ramp
This boat launch facility (Suttons Bay, Michigan) has a gently sloping ramp, a courtesy dock alongside, and a stable water level. The prominent sign on the end of the dock clearly prohibits "power loading."
Photo credit: LHG


Water Conditions

The slope of the bottom in the vicinity of a "Michigan" Ramp is likely to be the same as the ramp. The ramp is usually just a slab of concrete set on the natural bottom of the lake. The slope is often rather gentle, typically not more than about ten degrees of decline into the water. The water level of the body of water for a "Michigan" Ramp is generally stable and has no diurnal variations. It may change from year to year, but it does not fluctuate on a daily basis, nor does it change greatly from spring to summer to fall. The lake bottom is usually sand or loose gravel, which can be easily displaced by prop wash. For these reasons the length of the ramp is relatively short, and docks can be supported by pilings into the bottom (as opposed to floating docks).


The launching technique at the "Michigan" Ramp is to back the boat into the water on the trailer with no one aboard. Using gravity and a manual pull the boat is manuevered sternward and off the trailer, and made fast to the dock. The trailer is then driven to a parking area, the crew returns to the dock, and the boat departs the dock. The ramp is clear for the next user.

Recovery is the reverse. The boat approaches the dock and is temporarily made fast. The crew fetches the trailer. The boat is loaded onto the trailer manually, without power loading. The trailer then clears the ramp area.


Notice that it is possible to launch and recover single-handed. One person can handle all the launch and recovery chores using the "Michigan" Ramp style of operation. The only point in the process that is a bit hard to handle occurs just as the boat is loading or unloading from the trailer. If strong winds are present it is much easier to accomplish if an assistant can hold the boat lines and help keep it aligned to the dock during the time when it is partially on or off the trailer. A second person on the crew can be helpful, but they're not mandatory.

No Power Loading!

At almost every "Michigan" Ramp, operators of the ramp facility have large signs in place advising that power loading is prohibited. This restriction is in place because of concerns for the long term preservation of the ramp. Because the "Michigan" Ramp tends to enter water with a gentle bottom slope, if boats were to power load the prop wash would displace the sand and gravel and build it into a mound a few feet behind the end of the ramp. Eventually a rather significant shoal will be created by repeated power loading. The shoal then becomes a hazard for boats near the ramp area, where the sudden reduction in depth can mean a dinged propeller to the fellow without local knowledge of this artificial reef. Power loading can also tend to create a deep pit right at the end of the ramp. This is a problem for ramp users (if their trailer wheels back beyond the end of the paved ramp and into this pit) and for maintainers of the ramp (as the end of the ramp slab begins to be undermined and may not be sufficiently supported). For these reasons, a "Michigan" Ramp generally prohibits power loading and warns of fines, etc.

In order to get the boat on the trailer without using its engine, the operator must winch it to the bow stop using the "armstrong" method. This is usually not too hard because the slope of the ramp is fairly gentle. The gentle slope of the ramp also means that when the trailer is backed-in to the point where the trailer winch post is just at the water's edge, the far end of the trailer is not so deep that the stern of the boat is immersed to the point of floating free (although this varies greatly from ramp to ramp).

The "Kentucky" Ramp


The "Kentucky" Ramp is a launch facility where the ramp extends into the water by itself, with no dock at hand. There may or may not be an adjacent service dock. If there is a dock, it is not at the ramp, and it is provided more to facilitate temporary docking and loading of passengers than as part of the launch or recovery process. If there is no dock, getting on or off the boat while in the water is done by putting the bow ashore and scrambling over the stem.

Photo: Launch ramp, no courtesy dock
A "Kentucky" Ramp
This boat launch facility has a ramp, but no courtesy dock alongside. The water levels may vary with tides or other influences. The best practice in this situation is to launch the boat by driving it off the trailer. This beautiful 22-Revenge is about to go into the water on its all-bunk style trailer. (Although a "Kentucky" style ramp, this facility is actually on the Waccamaw River at Murrells Inlet, South Carolina.)
Photo credit: Charles Warren


Water Conditions

The water in the area of the ramp is often quite deep, with the bottom sloping rapidly down to depths of eight feet or more. This may mean that at the end of the paved ramp the natural depth of the water is greater than the ramp, so the ramp surface is built up on a foundation that extends up from the natural lake bottom. The water level at the ramp area of a "Kentucky" Ramp is often subject to seasonal variations over a considerable range. The water levels may be controlled by downstream dams, or subject to spring flooding. The water may also be tidal, and vary over a considerable range, requiring a very long ramp to accommodate all the variations. The wide variation in water level is one reason for not having a dock. The ramp may have to extend quite a way into the water during periods of low levels, and a fixed dock that was built to be above the high water range would then be much too high to be of any use. Problems like this are one reason the dock is not included at launching sites with extreme water level fluctuations.


The launching technique at the "Kentucky" Ramp is to back the boat into the water on the trailer until the engine is over water with sufficient depth to lower the engine. The engine is then started and an operator backs the boat off the trailer using the engine reverse thrust. The trailer is then driven to a parking area, and the ramp is clear for the next user.

Recovery at the "Kentucky" Ramp is the reverse. The boat loiters near the ramp while the trailer is brought into position to load. The operator drives the boat onto the trailer under power. The trailer is driven clear of the ramp.


Notice that it is possible to launch and recover single-handed, but it is much more efficient at the "Kentucky" Ramp to have two people. A single hander has many disadvantages. He must back the boat into water, then climb into it without benefit of a dock alongside. This usually means walking down the trailer central beam and climbing over the bow. Then, he has to start the engine. Then, he must go forward and release the bow strap. Then, he must back the boat off the trailer. Once the boat floats free he must find someplace to temporarily moor it while he returns to the ramp to get his trailer out of the way. If two people are involved it goes much faster. One drives the trailer into the water while a second, already aboard, starts the engine and backs the boat off. On recovery, one gets the trailer in position while the second drives the boat right on. If the trailer is positioned properly, the boat will be driven to the bow stop, the bow strap quickly secured, and the trailer driven clear of the ramp. Done by a well-rehearsed team, a boat can be loaded or unloaded in 30 seconds at the ramp.

Power Loading

The "Kentucky" Ramp really demands power loading and unloading. Without a dock at the ramp, it is difficult or impossible to control a boat by lines while it floats near the trailer. An alternative might be to wade into the water, but this is often unattractive because of the depth, temperature, and clarity of the water, and the age, inclination, and temperament of the operator.

Power loading is not a concern for for the ramp maintainers because often the paved ramp extends to a considerable depth of water, the bottom may be muddy and unlikely to be displaced as easily as sand or loose gravel, and there may already be a large drop off at the end of the paved ramp due to being built up above the lake or river bottom.

Ramp Summary

These, then, are the two general styles of ramp facilities. The "Michigan" Ramp has more facilities to maintain, as is has a dock. But the "Michigan" Ramp also wastes some of its ramp area by having the dock present. In contrast, a "Kentucky" Ramp may be just a broad paved area entering the water, with no space lost to docks at the ramp area. (In Paducah, Kentucky, we saw that the sloping and paved levee built to control Ohio River flooding was also used as a continuous boat ramp throughout the downtown area.)

Effect of Ramp Facilities on Trailer Performance

How does the type of ramp facility affect the type of trailer to be used? The two are really closely connected. There are many attributes of the two ramps styles that tend to make users prefer one style of trailer over the other. There are two kinds of ramps, and two kinds of trailers, giving rise to four possible combinations. Let's examine these four variations and see which ones work the best.

"Michigan" Ramp: Keel Roller Trailer

The combination of a "Michigan" Ramp and a Keel-Roller trailer is very workable situation. Because the ramp requires manual loading and unloading, the reduced effort needed to move the boat on or off the trailer is an advantage. Because the ramps depths may be limited, the need to only partially submerge the trailer will permit loading or unloading without difficulty at rather shallow ramps. Because the ramps have a dock right at the ramp, there is no problem created by the manual loading/unloading sequence in terms of getting on and off the boat if single handing. In summary, the keel roller trailer and "Michigan" Ramp are an excellent combination.

Photo: Launch ramp with courtesy dock, keel roller trailer
Keel Roller Trailer Launch
With the trailer backed down the ramp only to the point where the transom is just in the water, this big Whaler 25-Outrage is ready to launch. When the winch strap is released the boat will roll right into the water with gravity supplying all the force necessary. About a dozen keel rollers provide a low-friction rolling surface. The boat can be recovered with about the same attitude on the trailer. A two-speed winch provides plenty of mechanical advantage to lift the boat out of the water and onto the trailer via the rollers. This "Michigan" style ramp is actually in Tobermory, Ontario. Check out that water clarity. You can see 20-feet to the bottom in the harbour (!) and as much as 50-feet to the bottom in surrounding areas of Georgian Bay.
Photo credit: LHG


Photo: Launch ramp with courtesy dock, loading on keel roller trailer
Keel Roller Trailer Loading
After a spring day of walleye fishing on Lake Huron, Jim Gibson loads MEMORY onto his keel roller trailer with lateral bunks at a "Michigan" ramp. This ramp actually is in Michigan, on the Black River in Port Huron, and ironically it permits power loading, too. Note that the winch stand is over dry land and no wading is necessary. The boat floats on the back half of the trailer, then rides up and onto the keel rollers in the front half. An assistant on the courtesy dock steadies the boat with lines against a cross wind. The trickiest part of this operation is walking out on the trailer frame to attach the winch strap to the bow eye--good balance is an asset.
Photo credit: JWH


Photo: Launch ramp with courtesy dock, loading on keel roller trailer
Keel Roller Close Up
In order for a trailer to be suitable for use with keel rollers, it must have cross members. This CONTINENTAL trailer has five cross members. Paired rollers provide excellent support and low friction. The 19-Outrage II rolls easily onto the trailer. Another detail to note is the winch should be located so that it pulls upward on the bow eye. This will assist the boat in coming forward and onto the trailer. The winch pull should never be downward, as that will tend to bind the boat against the rollers.
Photo credit: JWH


"Michigan" Ramp: All Bunk Trailer

The combination of a "Michigan" Ramp and an all bunk trailer is a workable situation, but perhaps not the optimum. Because the ramp prohibits power loading, an alternative technique must be used. The trailer must be submerged to the point at which the boat can float on or float off. This may require backing in rather farther than one would prefer at some shallower ramps, putting the rear axle of the trailering vehicle into the water in some cases. This also tends to put the winch post in the water, meaning the operator must wade out to operate the winch (which must be used to haul the boat forward on the trailer or at least to make the winch strap fast). Water temperature and clarity can be factors which make that an unpleasant experience, particularly in spring and fall. Floating off is usually not a problem, but floating on can be more tedious. When floating on, most of the boat will not be in contact with the bunks. As the trailer is hauled up the ramp the boat will drop onto the trailer bunks, but there is no guarantee that it will position itself in perfect symmetry and squarely aligned to the trailer. Using the float on loading technique often means making several trips up and down the ramp, nudging the boat into alignment on the trailer. (Note to my critical readers: I am not making this up; one has only to go to a "Michigan" Ramp and watch boats being loaded on all bunk trailers to observe this phenomenon.) In summary, the all bunk trailer and "Michigan" Ramp combination is workable, but has certain disadvantages.

Photo: Launch ramp with courtesy dock, loading on all-bunk trailer
Bunk Trailer Loading--"Michigan Ramp"
California diver Chuck Tribolet has just loaded his 17-Montauk at a Pacific Ocean ramp with courtesy dock onto an all-bunk trailer. Note the location of the water line (shown by arrow) and the winch post just above it. The rear wheels of the vehicle are far up the ramp on dry concrete thanks to a very long tongue. Incoming swells often cause water to surge up these ramps. Also note how low on the trailer the boat is positioned, fitting between the wheels, not above them.
Photo credit: Chuck Tribolet


Photo: Tongue modification for all-bunk trailer
Tongue Modification
The tongue of this Shoreland'r trailer has been modified to permit removing it when parking or storing the trailer. This also permits a modest extension (18-inches) when needed on the launching ramp.
Photo credit: Chuck Tribolet


Photo: Rear view of all-bunk trailer showing low position of boat
Bunk Trailer Design
To permit all bunk trailer designs to work effectively, the boat must be carried as low as possible on the trailer frame in relation to the axles. A low position helps to get the boat floating on or off without having to bury the trailer underwater. Typically, this means the cross frames of the trailer will have to be vee-ed or curved. On smaller boats it is possible to fit the boat's maximum beam between the wheels. As boats become wider, however, this is no longer possible, and the boat must be carried higher on the trailer frame to clear the wheels and fenders.
Photo credit: Chuck Tribolet


"Kentucky" Ramp: All-Bunk Trailer

The combination of a "Kentucky" Ramp and an all-bunk trailer is an excellent one, where the strengths of one element complement the weakness of another. Backing the boat into the water with someone aboard is the best launching technique and solves the problem of no dock alongside. Loading the boat by driving it onto the trailer is much easier than trying to haul it in with a winch (when there is no dock alongside to moor the boat). If the trailer is positioned on the ramp to just the right point of immersion, the boat can be driven right to the bow stop and no winching will be needed. Further, once at the bow stop the boat will be so firmly on the bunks that it will not have any tendency to slide back. Then the bow strap can be secured quickly, and the trailer can be hauled immediately off the ramp. The action of loading under power tends to align the boat perfectly to the bunks, so there is seldom any need to reload to correct misalignments. No one needs to get into the water at any time, so this technique can be used in spring and fall when water temperatures are too cold for wading.

Photo: Trailer is deeply submerged at launch and recovery
Kentucky Ramp and Bunk Trailer
To facilitate getting the boat to float off the trailer bunks, the trailer is often backed into the water until the rear is submerged to the point where the boat floats free. With larger, deeper vee boats, this can mean putting the trailer well under water. The guide posts at the rear are very important to help aim the boat onto the trailer when loading.
Photo credit: Charles Warren


"Kentucky" Ramp: Keel Roller Trailer

The combination of a "Kentucky" Ramp and a keel roller trailer is a very workable one, but it has a couple of minor drawbacks. In general, all the techniques used with the all bunk trailer can be used with the keel roller trailer, except that careful attention must be given to when the bow strap is released and when it is secured. This is because there is a much greater tendency for the boat to roll off the trailer just from gravity than there is with the bunk trailer.

In launching, operators with a keel roller trailer will not be able to release the bow strap until the boat's stern is over deep water because of concern that the boat will come off the trailer while still on the ramp. (This is generally not a worry in the all-bunk trailer.) This means at launch someone will have to release the bow strap after the trailer has been backed into the water, which can make for an awkward process for the single handier.

In power loading with a keel roller trailer, the boat will not tend to stay at the bow stop. As soon as thrust is removed the boat will roll back in the water. Therefore someone must "catch" the boat as it comes to the bow stop and secure the bow strap. Again, this is difficult for a single-hander. (I have seen some operators leave their engine running in forward and exit the boat to secure the bow strap.!)

Other then these minor problems, the keel roller trailer will work well at a "Kentucky" Ramp.


Analyzing the results, it is seen that the least workable combination results from use of all-bunk trailers at a "Michigan" Ramp, where manual float-on/float-off loading is needed and ramps are shallow. The combination that produces the fastest potential ramp usage is the all bunk trailer and power loading at a "Kentucky" Ramp. This technique also minimizes any wading needed to load the boat on the trailer. The keel roller trailer is the most versatile, working well with any ramp situation, but at a "Kentucky" Ramp launch, the all bunk trailer will probably be more popular.

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Copyright © 2001 by James W. Hebert. Unauthorized reproduction prohibited!

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Author: James W. Hebert
This article first appeared November 25, 2001.
Added three additional photographs January 27, 2002.