Trailer sway

[warren631]

The Mac Bump doesn't seem to work for me. My trailer sways above 45 mph. I measured the tung weight and it was only 10 lbs so I put 3 x 50 lbs bags of sand at the front wall of the v-birth and now its about 200 lbs (don't know where the extra 50 lbs came from). So I guess I'm good. Haven't trailered it yet. Will it still float and sail?

[Sumner]

Are you trailering with the motor on? How is the boat loaded inside? I've always trailered with the outboard on but also have always had a lot of stuff inside upfront in or under the v-berth (lots of drinking water there).

Some with a single axle trailer have moved the axle back just a bit. Not a big job especially for a welding shop and a good time to put on new spring hangers along with new springs as they don't cost that much.

I added a second axle and a third bunk since I trailer with so much stuff in the boat.

Also I never like doing the Mac bump. Don't like the idea of trying to get that much weight to move forward under different circumstances.




http://purplesagetradingpost.com/sumner ... ds-17.html


I modified the "V-block' so that it is movable and use that now. It just takes a second to move it and I'm not trying to move the boat via the 'bump' anymore.

Sumner

============================
1300 miles to the Bahamas and back -- 2015

The MacGregor 26-S

The Endeavour 37

Trips to Utah, Wyoming, Idaho, Canada, Florida

Mac-Venture Links

[kurz]

If you don't want to move the axle but just want to put more weight in front: I would not put it IN the boat. But put it on the front of the trailer. So you will not have changes on the boat in the water.

But for longer use I'm shure you will be happier if the trailer an tongue weight is corrected without additional weight but with the right position of the axle.

[Tomfoolery]

On road trips, I carry a lot of relatively heavy things, like the full enclosure in a big equipment bag, bottled water, 50 ft. electric (hydro) power cord, stuff like that, and I move it all to the vee berth, just for trailering. It gets redistributed once I'm there, and since I'm going to bring it all anyway, no extra weight is needed. It's a few hundred pounds (guessing), most of which ends up on the hitch, in addition to the couple of hundred that's there when the boat is empty for the winter.

I sometimes forget to move the heavy stuff before flooding the ballast tank, which makes it overflow out the vent under the vee berth with the bow extra heavy, and which is also piled high with stuff so it's hard to get to the vent to check and plug in a hurry when it dawns on me, so it's a double whammy, but that's on me and me alone. Had to do a little mopping up at the last MMOR in Lake Simcoe.

[1st Sail]

IIRC from past posts there were two basic rules so to speak. Tongue weight not to exceed 10% of loaded weight. Hitch to axle distance not to exceed 150% of tow vehicle wheel base. I believe there are some post regarding improved highway stability with dual axle trailers. My 26M with single pulls like it is on rails with my Yukon XL. But then I'm clearly within the parameters of tongue weight and axle ratios.

[Sumner]

IIRC from past posts there were two basic rules so to speak. Tongue weight not to exceed 10% of loaded weight.....

I believe that it is recommended that tongue weight is at least 10% of the trailer weight. If you go over that or even if you are at 10% the determining figure is what the tow vehicle and it's hitch are rated for. One thing I like about our Suburban as a tow vehicle is that it and the hitch can handle a lot of tongue weight and it helps for a stable tow. One other thing to consider is if the tongue itself if up to more weight forward vs. back over the axle/axles.

The last thing go consider is having weight far aft on the trailer, even if you have tongue weight, can cause a pendulum effect and if the trailer starts to sway it can get worst real quick. You don't want the back of the trailer to gain side to side momentum. Coming back from Florida the last time I still had quite a bit of gas in the 19 gallon tank in the laz, the laz was full and I of course had the 9.8 HP on the stern and the 3.5 HP outboard mounted on the side of the stern. I had towed a few hundred miles and was up in the FL panhandle and started going down a hill and the trailer started to fish-tail. I got stopped, gradually, and took the small outboard off and moved it forward along with a few items in the laz and never had a problem the other 1900 miles home. Sometimes it doesn't take much to upset a loaded trailer.

Sumner

============================­
1300 miles to the Bahamas and back -- 2015

The MacGregor 26-S

The Endeavour 37

Trips to Utah, Wyoming, Idaho, Canada, Florida

Mac-Venture Links

[Catigale]

Speed is the other factor. I've found the boat is rock solid at 60 mph, that is my new trailering max speed.

At 70mph, it is a different beast. I suspect that's windage.

At 60 mph, I cruise the entire Mass pike to the Cape on cruise control in the right hand lane, painless

[Tomfoolery]

Speed is the other factor. I've found the boat is rock solid at 60 mph, that is my new trailering max speed.

At 70mph, it is a different beast. I suspect that's windage.

At 60 mph, I cruise the entire Mass pike to the Cape on cruise control in the right hand lane, painless

Having done a number of long-distance hauls now, the last one being the Thruway and the Mass Pike (I-90, for those not from here) from Rochester to Cape Cod, that has been my experience too. 60 mph in the right lane on cruise control, and all's right in the world. Over 60, and it starts getting a bit white knuckle-y. The trailer seems to rapidly get more sensitive to inputs from the steering and from cross winds with speed, but at 60 and down, it's all pretty relaxed.

I'm pretty sure it's not just in my head, either, as when I cross the border into Canada and change the speedometer to km/hr, I've noticed that I naturally hang around 95-96 km/hr, not at that nice round 100 km/hr number, as that just seems to rapidly veer into the less-stable, more attention required zone.

I have a two-axle trailer, by the way. But my Jeep Grand Cherokee, even though it has a 7200 lb tow rating, has a short wheelbase, and it really doesn't feel stable at higher speeds with that trailer, so 'slow is pro' applies to trailering as well as docking.

[warren631]

Sumner has an adjustable V-block mod. Does that stop trailer sway? If I tie the front of my boat very rigidly to the trailer so it couldn't move side to side would that stop sway?

[Tomfoolery]

Sumner has an adjustable V-block mod. Does that stop trailer sway? If I tie the front of my boat very rigidly to the trailer so it couldn't move side to side would that stop sway?

Moving it forward into the existing vee block would shift the tongue weight up a bit, which works to reduce the tendency. Part of the issue with Macs on OEM trailers is that when the boat is in the vee block as it comes up the ramp, it rotates away as the boat takes the angle of the trailer. Hence the "Mac Bump®" to move it back into the block. (illustration below)

If you were to make the vee block adjustable, then you could move it forward some significant distance so that when the trailer rotates level, the boat would be in the right spot for tongue weight. Then move the vee block back to contact the bow and lock it down prior to hitting the road.

Sumner worked some magic in this area, but I just don't recall the details.

On a related note, the pole tongue on the OEM trailer, while structurally adequate for the load, is a bit flexy. If the boat is not in the vee block, it's noticeably 'springier' and the bow dances about on the road. Getting it into the vee block stiffens it up a bit. One of these days I'll reinforce it, but being wiggly or twitchy has nothing to do with sway, so it's not high on my list of priorities.



As an interesting aside, when looking at the sketch, it's obvious that if the boat pulls away from the vee block as the trailer is hauled up the ramp, the opposite would be true when splashing the boat. If the bow is tight to the vee block (from the Mac Bump®, of course) and the winch line isn't slackened before the stern hits the water, when the trailer travels down the ramp and the boat stern floats (rotating the boat upward at the stern, opening the angle between them), the rope or cable will get tighter, and potentially damage either the winch, line, or even the U-bolt in the bow. I always put 6" of slack in it before it hits the water (with the chain removed first, of course) so it can't get a head of steam and stop hard if I go a little too far in, but it won't fetch up tight, either. Just sayin'.

[Sumner]

Sumner has an adjustable V-block mod. Does that stop trailer sway? If I tie the front of my boat very rigidly to the trailer so it couldn't move side to side would that stop sway?

No, not in itself, but if the boat is back just a little ways it can cause sway in some cases.

I've not had problems in general with 'sway' since...



... going to the second axle but the last time coming home from Florida I got sloppy loading the boat and didn't have the weight forward in the boat that I usually do and the boat started to sway once on I-10 in Florida. I stopped and took the 40 lb. dingy outboard off the back and put it forward in the cockpit and no problems the other 2000 miles home. I usually have the 40 gallons of water filled under the V-berth and didn't have much there when this happened and had heavy items in the Laz.

I had the same thing happen with a 2 axle U-Haul trailer once with it loaded to the ceiling front to back. The trailer swayed bad and I took less than 100 lbs. out of the very back of the trailer and moved it to the tow vehicle and no more problems.

With that in mind sometimes a very small amount of weight can be a big influence especially if it is at one end or the other of the trailer. So having the boat back 6 inches in the bunks could possibly cause sway in some conditions. If your tow vehicle is capable of more tongue weight move more weight forward in the boat and keep heavy things off the stern if possible,

Sumner

============================
1300 miles to the Bahamas and back -- 2015

The MacGregor 26-S

The Endeavour 37

Trips to Utah, Wyoming, Idaho, Canada, Florida

Mac-Venture Links

[Tomfoolery]

It would probably help in my case if I didn't travel with both 6 gallon tanks full, and stored in the stern in their cubbies. Either empty, or moved to the cabin, but I just don't like putting fuel tanks in the cabin. Not for safety, as batteries are disconnected at the switch, but more in case of a leak or splash, which would stink the place up.

I just don't care for showing up some place and having to look for gas, especially ethanol-free gas which isn't available everywhere.

85 lb or so (75 lb for 12 gallons, plus 10 lb for two plastic tanks) that far back contributes to an aft-shifted CG, plus it's mass in the ass, which contributes to a larger angular momentum.

[BOAT]

Speed is the other factor. I've found the boat is rock solid at 60 mph, that is my new trailering max speed.

At 70mph, it is a different beast. I suspect that's windage.

At 60 mph, I cruise the entire Mass pike to the Cape on cruise control in the right hand lane, painless

Having done a number of long-distance hauls now, the last one being the Thruway and the Mass Pike (I-90, for those not from here) from Rochester to Cape Cod, that has been my experience too. 60 mph in the right lane on cruise control, and all's right in the world. Over 60, and it starts getting a bit white knuckle-y. The trailer seems to rapidly get more sensitive to inputs from the steering and from cross winds with speed, but at 60 and down, it's all pretty relaxed.

I'm pretty sure it's not just in my head, either, as when I cross the border into Canada and change the speedometer to km/hr, I've noticed that I naturally hang around 95-96 km/hr, not at that nice round 100 km/hr number, as that just seems to rapidly veer into the less-stable, more attention required zone.

I have a two-axle trailer, by the way. But my Jeep Grand Cherokee, even though it has a 7200 lb tow rating, has a short wheelbase, and it really doesn't feel stable at higher speeds with that trailer, so 'slow is pro' applies to trailering as well as docking.

I have questions on that - I will send you a PM.

Towing 'boat' with my 22 foot sprinter van is about the same a not towing anything - the boat has no real effect at all until I start to climb hills and then I feel it on the motor - but there is never a sway or anything like that at any speed - even at 80 mph (the downhill part entering San Juan Capistrano on the 5 freeway towards Can Clemente to Oceanside is 7 lanes both sides and can get pretty fast - the cars go 85 and I am going 78 just to prevent me from holding up traffic in the slow lane!) I can't even feel the boat behind me so I am a bit concerned about things I'm hearing about other cars here. I need some advice.

[Tomfoolery]

Probably the biggest thing in the case of your Mercedes Sprinter is that it has a 144" wheelbase, while my Grand Cherokee has a 114" wheelbase. That 30" is a big deal.

The rest I detailed in an email.

[BOAT]

Probably the biggest thing in the case of your Mercedes Sprinter is that it has a 144" wheelbase, while my Grand Cherokee has a 114" wheelbase. That 30" is a big deal.

The rest I detailed in an email.

Thanks tom.

These two cars are actually the same car chassis built in the same factory but with different engines, (and a lot less leather):




The bottom car is what mastreb drives and he had high praise when he towed his MAC from California to New York. I am a big fan of German cars so I thought I wanted one too.
BUT,
The top car is 20 grand cheaper, (mastreb is a lot richer than me), so I figured it would be a good backup tow for 'boat' and a grocery getter for the wife, and I can do a lot with 20 grand...

I know that sway is compounded by a short wheelbase but mastreb said it was diminished greatly by having the rear wheels of the car very close to the trailer hitch (as in the case for the cars pictured above) - and thus reduced the leverage the trailer had on the rest of the car.

I would be curious to see if adding the weight to the front of the boat/trailer eliminated the sway issue mentioned in warrens post - we need an update from warren.