SJ23 Tech Tip A10, (Updated 2025-08-30) Bob Schimmel, Robert Trower, Randy Cook, & Robert Hasegawa.

Index

SJ23 Trailer Components, Maintenance, Weight Distribution & Dimensions.

COMPONENTS                   - Capacity Plate, Weight, Lights, Break-Away System, Axles, Fenders, Keel Support, Guide Posts, Bunk Boards,
                                                           Trailer Winch Tree, Trailer Bow Support Roller, Draw Bar, Coupler.
MAINTENANCE                     - Nuts & Bolts, Paint.
WEIGHT DISTRIBUTION  - Align Support Pads, Trailer Dimensions.

Panache's trailer was manufactured in 1979 by EZ Loader Trailers.  The descriptions that follow in this Tech Tip are about this trailer.  You should be able to "reverse engineer" these dimensions for another manufacturer trailer without too much difficulty.  You should also read Tech Tip A01, Desirable Features of an SJ23 Trailer.

 TRAILER COMPONENTS

LEGALESE & CAPACITY PLATE - The trailer capacity plate is shown here.  If you cross the 49th parallel, you MUST have a capacity plate attached to the frame and have proof of ownership in hand.  If you don't own the trailer you better have a signed and dated letter from the owner (include date, owner address and phone number) giving the named borrower permission to use trailer registered with VIN# till and end date.  In the body of the letter state where you are going, the purpose of the visit and how long you intend to be on the other side of the border.  Customs people can be real picky, so smile when they ask you.   TOP  

OVERALL WEIGHT -  An SJ23 requires a minimum of 2 long fixed support bunks or 4 articulating support bunk boards on the trailer, a keel support and a V-block or roller on a "winch tree" to pull the hull up on the trailer and to stop the hull when braking.  Assuming the total weight of an empty SJ23 is 2700 lbs, of which 960 lbs. is ballast, the 4 support bunks must each carry 435 lbs. or each bunk board 870 lbs and the keel support will hold 960 lbs.  Simple enough math but somewhat difficult to measure with a scale.  In addition to this weight you should allow for about 500 lbs of "stuff" on board, rigging, rum, gum, scotch, food, beer, a life jacket, basically all the staples needed to sustain life!  One final point, some SJ23s came out of the factory heavier than the ~2700 lb. design limit.  So heavy that they required a tandem axle trailer.  Yours may be one of them so don't rule this out.   TOP  

LIGHTS - An SJ23 trailer requires three types of illuminated lights if it is to be towed on a public road; signal lights (brakes, left & right), a band of 3 horizontal lights in the center of the frame indicating it is wider than 80", clearance lights to mark the width of the trailer to passing and opposing vehicles and a licence plate light.  I'm not sure if clearance lights are required on the fenders, being the widest part of the trailer.  In my experience fender lights take a beating so I use passive reflectors.  Regardless, orange in front and red to the back.  See Tech Tip A08 for electrical maintenance.   TOP  

AXLES & SUSPENSION - This EZ Loader frame is made of (3x4)" rectangular steel tubing 1/8" thick with all components bolted together.  It was factory equipped with a single 3500 lb. (1588 Kg) straight axle on springs equipped with 10" electric brake drums.  When radial tires finally appeared on this continent I installed the highest load rated tires that could fit the rims, P235x75R15.  This combination can support an empty SJ23 but it is close to its limit.  This is one of the reasons why I converted the trailer to tandem 3500 lb. axles.  See Tech Tip A04 and A03 for a description of the conversion.  If you want a tandem axle then each axle should have a GAWR rating of >3500 lbs (1588 Kg), not 2000 lbs.  If a tire blows on a 3500lb. axle then the other axle has a fighting chance to support all the weight till you stop.  Brakes are mandatory with a GVWR of 6000 lbs.  All wheels have drum brakes. 

The trademark construction of EZ Loader trailers is to bolt all components together so it can be adjusted to support most any shape load and weight.  Welding may be cheaper than bolts but you'll appreciate the bolts if you ever have to adjust anything.  This feature has its price which means you have to inspect the nuts on a regular basis.  I use an old race car technique and applied a dab of silicon sealant between each nut and the exposed thread.  That ended my worry of nuts turning loose.  Checking the trailer annually should be part of your routine safety inspection.   TOP  

BREAK-AWAY SYSTEM - See Tech Tip A01.   TOP  

FENDERS - There are two sets of steel straps to support the tops of the fenders and two more at the bottom of each fender, one at the front and the other at the back.  You can just see a set inside the left fender above.  With four straps supporting each fender they no longer vibrate at highway speed.  I don't allow anyone to step on them, including myself!   That's what the aluminum ladder lashed along the front of the trailer is for.   TOP  

KEEL SUPPORT & GUIDES - The combination keel support with keel guides, (1.5x3)" steel tube, is visible across the middle of the trailer above.  The bottom of the keel guide is lined with soft cedar and the sides of the keel guides are lined with slippery UHMW.  Since the keel support bar is adjustable (up/down) with the crank shown at right, I raise the bar up to the keel to support ~600 pounds of it.  This offsets some of the weight on the support bunks and the hull.  This creates the correct dimensions between the keel support and the hull support bunks.  For reference purpose, the bottom of the keel rests just below the bottom of the trailer frame. 

NOTE - I grease the thread so it is easy to adjust the bar to full height.  If I eat my Wheaties in the morning I can jack the hull up off a bunk to slip cardboard in the gap of a support bunk.

I think the original owner of the trailer added this bar.  The hand crank is strong but has all the hallmarks of a DIY mechanic.  Its a nice feature though.   TOP  

GUIDE POSTS - Guide posts service to direct the floating hull over the trailer so the keel support can grab the keel thereby ensuring the hull is centered on the trailer.  See Tech Tip A01.   TOP  

FIXED or ARTICULATING BUNK BOARDS - Panache's EZ Loader Trailer is equipped with four fully articulating support bunks that each consist of two pressure treated (2x4)"s that you can see above.  Each bunk can rock left/right on top of its mounting post and each (2x4)" can be rolled independently to fit flat against the hull.  Once the (2x4)'s are aligned to the hull I lock them for stability and ease of launching.  There is such a thing as too many adjustments on the launching ramp!  This is definitely a time to leave well enough alone.  Each pair of posts can rock fore/aft on a common cross bar hinged from the bottom of the side rails.  Together the bunks align perfectly to the hull.  In addition, each post can be adjusted together or apart to stabilize the hull.  I calculated that the four bunks actually provide more support than two full length 6" bunk boards due to their perfect alignment with full contact.    TOP  

TRAILER WINCH TREE & BOW ROLLER (1999) - I beefed up the original flimsy winch tree because I thought it wasn't rigid enough to pull the hull up the trailer or support the bow while towing.  It wasn't difficult to visualize the boat coming into my "glove compartment" during hard braking.  The second reason was to stiffen the frame for road hauling.  I've always wonder about those pathetic winch posts without angle bracing.  In reinforcing the tree I replaced the short post with a taller one to raise the winch above the boat trailer eye.  This so the boat trailer eye can fit snug under the tree roller.  See Tech Tip A01.
In this photo I'm slipping the jib downhaul ring over the forestay after we stepped the mast.  I tend to forget this job at the ramp.  This is many years before I added roller furling to Panache.   TOP  

BOW SUPPORT ROLLER (2000) - The 8" wide roller shown under the bow below works in conjunction with positioning the trailer eye under the roller.  It is an important addition I added a few years later.  It guarantees perfect fore aft positioning of the hull for every haul out regardless of the slope of the ramp.  See Tech Tip A01 for a description.  It was installed ~6' back from the boat trailer eye.   TOP  

DRAW BAR (1999) - EZ Loader designed this trailer with a single draw bar.  The short overlapping joint that connected the draw bar to the side rails was too weak due to being only 20" long.  Probably adequate for a power boat this trailer could also be used for but woefully inadequate for the 2700 lbs. of sailboat it now carries.  This joint flexed too much for my liking so I replaced the original 60" long draw bar with a 124" long bar, creating an overlapping joint of 64".  The inboard end of the draw bar is U-bolted to a new cross member of angle iron that is also U-bolted to each side rail.  As a result the joint no longer flexes. 
About 1.5' forward along the draw bar is another cross member where the new bow support roller was installed (2000).  I was able to install a fixed height roller to fit the spot because the rest of the bunks were already adjusted correctly.  If the bunks weren't correct the roller height would have been adjustable. 
Since the longer draw bar sticks out ~2' further at the front I can push the trailer into deeper water without doing the same to the Jeep.  I always raised the tailgate of my Jeep Cherokee for visibility on the ramp and now drop the tailgate of my Tacoma.  The extra walking space between both vehicles sure makes life easier on the loading ramp.  It tows more stable at highway speed.    TOP  

COUPLER - The 2" coupler is not of much interest to this Tech Tip except that you should be concerned if the coupler is only welded to the frame.  Some welds look pretty but aren't strong.  It takes a trained eye to know the difference.  Therefore, it's a good idea to back up the welds by thru bolting the coupler to the draw bar.  The bolts are a good backup to welds that can rust.  With the single draw bar configuration of this trailer, the only benefit an equalizing hitch offers is load distribution of the tongue weight.  While this works well, there is no roll stability since the torsion bars are parallel to each other.  I thought the lack of roll stability might limit the towing performance but it hasn't.  This could be because the maximum speed I tow is 100 K/H (60 M/H)! 

 MAINTENANCE

• NUTS & BOLTS - All the components on an EZ Loader Trailer are bolted together for easy alignment to different hull shapes.  With routine dipping in water the nuts will seize on the thread.  This makes it near impossible to twist a nut to adjust the trailer.  For this reason I dribble ATF on the thread around each nut.  I include the lug nuts on the wheels which is a lesson I learned when helping a guy with a flat tire on the highway.
• PAINT - The real reason for a coat of paint is to prevent rust.  The fact that a fresh coat impresses the dock watchers at the ramp is another issue all together.  Panache's trailer was painted white from the factory which was always prone to rust.  So I knocked the rust off, treated the spots with rust converter and painted the trailer black, especially the bottoms of the rails.  I chose black Tremclad because the sun heats it very quickly to dry the metal and prevent rust. 
  - I prefer a matt or satin finish because dew drip off quicker.  This finish also reflects some light, making it easier to see in the dark than flat paint.  I'm gradually painting over the flat paint shown in this photo. 
  Tremclad must be painted with a brush or sprayed with an airless gun operating at ~50 psi.   If the viscosity is too thick then thin it with paint thinner.  The thinner is also used  to clean the gun at the end of the job.  The trailer gets a light coat every 5 years and I've had little rust since. 
  - By the way, the ONLY way to paint a boat trailer is with an airless spray gun as it can get into nooks & crannies that a brush cannot.  In addition, I'll guarantee you at least half a dozen bruises on your shins and cut knuckles if you use a brush.  Don't ask!
• BUNK BOARDS (2025) -  In mid summer I returned to Panache's trailer for some routine maintenance and was surprised that the wood support bunks were damp.  Too damp for my liking as this could lead to wood rot.  This condition was aggravated by the fact that the trailer is parked in the shade during the summer, facing directly into the prevailing weather.  The shade has always been good for the tires though.  I returned during a hot spell, knowing the bunks would be dry, and covered them with the 4 small tarps, BBQ style.  The bottoms are left open to keep the bunks dry, which they did for the remainder of the summer.  The covers look sloppy because the mosquitoes were vicious and I was not about to sacrifice myself to these blood thirty invaders. 
• COVER BUNKS WITH RUGS (2025) - See Tech Tip A01     TOP

 WEIGHT DISTRIBUTION

TRAILER DIMENSIONS & POSITION of SUPPORT BUNKS for CORRECT WEIGHT DISTRIBUTION.
(A huge debt of gratitude goes to the guys who helped proof read these dimensions).

HULL FORE/AFT POSITION RELATIVE to the AXLES - To provide adequate hitch weight for stable towing, position the mid point of the hull (front of the large window) directly over the axle of a single axle trailer or over the walking bar (between axles) of a tandem axle trailer. 

KEEL SUPPORT BAR RELATIVE to the HULL -  The keel support bar is positioned midway between the axles or the front of the large window.  This is at the maximum girth of the keel which is 7.5" wide.  The boat rests on the trailer with the bottom of the keel flush with the bottom of the frame.

TRAILER BOW ROLLER RELATIVE to the BOAT TRAILER EYE - For easy, quick hassle free ramp launching you want the boat trailer eye to rest snug UNDER the roller on the tree when the boat is level on the trailer.  Therefore the winch line goes UNDER the roller.  This allows the boat to slide into the water unimpeded during launch time.  (In the 1990s I replaced the V-block with a roller to reduce wear and friction.  See Tech Tip B26.  I had to build a much taller and beefier tree to raise the winch above the boat trailer eye.)  The added advantage is that when the boat trailer eye is resting UNDER the tree roller, you know the boat is positioned correctly on the trailer.  A very convenient reference mark when retrieving on the ramp.  In addition, the trailer tows quieter when the boat is snug up against the winch tree.
The winch must be placed a few inches above the roller so the hull is pulled up and forward as it is comes to its final resting spot on the trailer.  The pivot bolt of the winch measures at 41" above the frame.  The boat is retrieved by floating it on the trailer as the winch and boat trailer eye cannot pull 3000+ pounds of weight up the support bunks.  There is too much friction for that much weight.  See Tech Tip B26. 

(Measurements shown below are to position the hull on the trailer)

________________________________________________

IMPORTANT - DO NOT make your trailer to the exact dimensions shown below.  I tried to take accurate measurements but since I was measuring on my own, they are likely off a bit.   So allow for adjustments to fit the hardware to your boat. 

The four support posts on my trailer form a rectangular box that is approximately (48 x 70)" and 16" deep, relative to the bottom of the keel.  The keel support resides at the bottom of that 16" deep "box". 

• BUNKS FORE/AFT - The posts, or centers of the bunks, should be about 70" apart (front to back) so the weight is distributed equally over the front/back bunks.  This is a compromise to support the hull without a keel support.  This would make a bunk board about 94" long.  This spacing optimally supports the keel and overhanging ends.  Relative to the boat, the center of the front bunks touch the hull 1 foot aft of the mast step and the back bunks under the companionway bulkhead.  These proportions work in conjunction with having an adequate support under the 900 lb. keel so the hull is relieved of having to carry the ballast.  Having adequate support for the keel is very important for long-term storage and is probably THE best reason to empty the boat while it's on the trailer. 

• BUNK SPACING - The posts should be about 44" apart (across the trailer) so the hull doesn't rock sideways.  Any wider than this and the bunks provide too much lateral support and not enough lift.  The posts could spread apart with the hull crunching down through the middle. 

• BUNK HEIGHT - The front and back bunks must be approximately 16" high relative to the bottom of the keel.  Leave room to adjust the height of the bunks. 

• KEEL SUPPORT - The keel support bar must be just above the top travel of a single axle so it does not stop the upward travel of the axle.  It can be placed between the axles if you have a tandem axle trailer. 

NOTE:  Every towing combination is unique.  The above dimensions are from my trailer and will get you in the "ball park" for yours.  They suit the hauling requirement of my short wheelbase Jeep Cherokee equipped with 4L engine and 5 speed.  Since I replaced it with a 5 speed automatic Toyota Tacoma, towing is much smoother and easier.  To date there are three copies of my trailer rolling around out there.  My trailer tows very stable at 100KM/H (60M/H) and you have absolutely no reason to go faster than that!    TOP  

ALIGN THE SUPPORT BUNKS -  The simplest method of guaranteeing proper weight distribution is to align the bunks to the hull, something that cannot be done with the boat off the trailer.  Failure to do this correctly will result in straining the hull around the support bunk and quite likely damage it over the long term.  Note Glen's comments below.

• "A frequent failure on an SJ23 are the flimsy, non-structural bulkheads adjacent to the mast compression post.  These bulkheads are mostly a divider between the V-berth and the settees.  This joint often fails after a few big bumps going down the road on a trailer.

• Another area that tends to be soft is the centerline of the floor just aft of the keel.  This area has no substantial bulkhead to help stiffen it.  Trailering, grounding, or sailing could transfer a keel load up into the deck or cockpit.

• Having a boat sit on a trailer with excessive keel loads for a long time in hot summers allows the boat to essentially melt onto whatever trailer form is beneath it.  All fibreglass boats do this.  A repair trick for big dents is to heat the surface with a heat gun and the tooling memory usually returns the hull to the original shape.  Then you fix the trailer!"  Gleno.
  - See Tech Tip B28 for someone who repaired a dented SJ23.

There are three key factors to align the four bunks or two bunk boards correctly so the hull weight is distributed equally amongst them. 

• BUNK SPACING - If the bunks are too close together (side to side) the boat will rock sideways at highway speed.  If the bunks are too close together (front to back) then the boat will hobby horse going down the road.  Position any of them too close together and the hull may roll off the trailer if stopped too hard or angled too much on the launching ramp.  Either situation is wee bit disconcerting, to say the least.

• BUNK HEIGHT - The support bunks on some trailer are so out of adjustment with respect to the height of the hull that you have to wonder what damage is being done.  When someone reports this problem it is usually about a vessel that has been neglected for a "zillion years" in a barn somewhere.  The person usually adds that there is a definite depression in the area of the rollers and the hull is pushed in a bit (soft or mushy).  The worst situation is when one of the bunks is higher than the rest.  It holds more weight and pushes harder into the hull. Not good.  Conversely if one bunk is lower than the rest, the hull is inadequately supported in that quadrant.  Bunk boards are equally as guilty with this problem. 
  The source of this problem is somewhat perplexing because if the hull is symmetrical (left to right) and touching the hull, then why aren't the bunks set to equal height?  Especially since it's fairly easy to adjust the bunks to the hull when the boat is sitting on the trailer.  In fact, this is the best time to make those minor adjustments, to make her sit just so.  You can resolve this problem by measuring the height of the bunks when the boat is off the trailer.  It will confirm that the bunks are equal height and therefore supporting equal weight. Mine looked OK until I measured them, only to discover that both starboard bunks were 1" lower than the port bunks.  No wonder the boat couldn't sit level when centered on the trailer.  This demonstrates how deceptive this problem can be.  Measure, don't assume.  Then sometimes I see a hull that sits so crooked on a trailer that you have to wonder about who loaded the boat or why this was done.  This problem is more associated with the operator than with the design of the trailer as it is due to poor placement of the boat on the support bunks or using bunks without adequate padding.  It looks so pitiful and it's such a shame to abuse a good craft like a San Juan sail boat. 

• BUNK SIZE - Rollers, while convenient for launching, are generally too few or too small to adequately support a fully loaded sail boat.  The pounds per square inch loading on rollers is too high for long term storage.  This is why bunk boards are used for a sailboat.  On most trailers the size of the bunks are within the pounds per square inch rating of the hull.    TOP  

BOAT OFF TRAILER - I rocked the boat on my trailer after my alignment described above and wasn't satisfied the bunks were supporting the boat equally. A quick trip hauling the boat down the highway confirmed this.  I could almost slip my hand between one bunk and the hull.  Obviously the hull was moving on the trailer and not settling well.  Something was out of whack and it is difficult to assess the bunks with the boat on the trailer.  The following steps describe how I fine tuned the height of the support bunks after the boat came off the trailer.  You can use my final dimensions in step 5 as a starting point to adjust the bunks on your trailer.  When you measure the height of the support bunks;

1. If the ground is absolutely flat and level, like an aircraft hanger, you can measure the height of the trailer frame and each bunk from the ground.  Park the trailer on smooth level pavement or concrete and measure the frame to ensure it is parallel to the ground, fore/aft & sideways.  This is assuming the frame is not twisted, same size tires all around and all springs are at the same height.  If the ground is rough you have to measure the bunks with respect to the top of the frame.  A lot more difficult to do.

2. To confirm that the trailer frame is straight and on an even plane (not twisted), measure the distance from the ground to the top of the frame, all around the trailer.  If all measurements are the same, you have a straight frame.  It's amazing the number of twisted trailers out there.  Another measurement that could be made is to stretch two strings diagonally across the frame.  If the strings just barely touch at the crossing, you have a very straight frame.  This is an extremely accurate method but it is difficult to find a couple of clear shots across the trailer for the strings.  It's worth doing though, if for no other reason than a check.

3. Confirm that the side rails are parallel (left/right) to each other by measuring the distance between them.  Many single axle trailer frames are not parallel because it is not as critical.  It is absolutely imperative that the side rails of a tandem axle trailer be parallel.

4. If the trailer frame is straight and the rails are parallel, you can safely measure the height of the bunks from a straight edge placed across the frame, which is now a very accurate reference, or the ground if it is absolutely flat like a hanger floor.

5. The centre of each support bunk should be about 19" (+ or - 2") above the bottom of the keel. 

After this initial alignment followed by another with the boat on the trailer, the hull has never moved on the bunks as I travel down the road.  It just settles in there and stays.  Sure makes for relaxed driving.

It should be noted that Panache's trailer is equipped with four fully articulating bunks, a trailer bow support roller, an adjustable keel support bar and a very sturdy roller on the tree.  The dimension of each "bunk" is (24x42)" and consist of two lengths of pressure treated (2x4)" covered with rug (bottom left open).  The full articulating feature ensures they align perfectly to the hull at all stages of a ramp launch.  I can't emphasize enough how important it is that the pads align to the hull.  The trailer is extremely stable at highway speed.   TOP  

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