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Catalina/Capri 25/250 Sailor's Forums

Catalina 250 Specific Forum

Porpoising

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Initially Posted - 09/10/2006 : 01:36:23

Rita & I are towing our 250 WK with a Ford F-250, tow package, etc. and the whole rig does a fair amount of porpoising as we drive. I can watch the bow of the boat bouncing up and down in my rearview. It's most noticable when we're going slower and on bumpier roads, which makes sense. We've tried moving stuff to both the v-berth, and the aft berth to distribute the weight, and neither seems to make much difference, we still get the porpoising effect. When we're on nice asphalt roads, and at speed it's nowhere near as noticable.

Does anyone have any advice how to rectify this, or at least damp down the oscillations?

Thanks,

David
C-250 Mainsheet Editor

Sirius Lepak
1997 C-250 WK TR #271 --Seattle area Port Captain --

Edited by - on

Turk
Admiral

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USA
736 Posts

Response Posted - 09/10/2006 : 06:52:03

Wow! I pull my WK with a Ford 150 and do not have the porposing problem you speak of. My only thought is not enough tongue weight, but as you said, you've moved weight up front. Have you removed your outboard? Shouldn't really be pulling it around over much distance with it on anyway. Is the trailer level? A 250 may need a receiver that drops 4" to level out the trailer. I use a drop reciever on my 150.

Some here have suggested using sway bars to help stabilize the trailer. I have never had a problem pulling mine without bars and have traveled 1000 miles at a time with no problems. I also pull an 18 ft traler with a ford 3000 tractor and brush hog on it (total:7000 lbs) and will tell you several inches forward or backward can really make a difference in the stability. I have a mark on that trailer exactly where the front axel of the ford tracter has to be at.

My best guess is that your trailer is not level. Let us know.

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Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 09/10/2006 : 07:43:36

Wheel base and weight of tow, condition of shocks, height of hitch, tongue weight and tire pressures all come into play. Likely most 250s suffer this to some extent and as you point out, road conditions can play big.

A few years ago, there was a section of interstate west of Little Rock that would absolutely hobby horse my otherwise stable rig.

A F250 has a long enough wheel base to provide a great tow. If however it has a lot of miles on it, the shocks may be gone and even though it may have stiff springs, shocks are what dampens hobby horsing so possibly they need replaced on both front and rear.

Check the ball height, it should be in the area of 17 inches... if considerably more or less, adjust it some way by inverting the ball on the bar or aquiring a new bar.

Check the tongue weight that it is not excessive. 10-15 percent is the rule. That would equate to between 500-800 lbs so if over, reduce or even bring the weight closer to the lower end as long as no sway is introduced by doing so.

Tire pressures on both tow and trailer should be raised to maximum specified for the tires while towing. However, some argue that running the back axle on the trailer about five pounds more yields positive results.

After these steps, if the problem remains, then it may have to be dealt with by an equalizing hitch, which almost certainly will solve the problem but at greater expense and trouble.

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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 09/10/2006 : 09:25:45

Arlyn & Turk,
Thanks for the pointers. The trailer is level with the drop hitch I'm using, the P-PO installed a fore & aft level gauge on the outside of the head above the drop board keepers, and it seems to be pretty accurate. I haven't put my big level on the trailer to actually check it, but I'm pretty confident that it's within tolerance. Before we towed it back from Bend (about 360 mile SSE of here), I took the whole rig to a tire dealer and had them check & inflate all the tires to close to their maximums (we'd been on the road for about 40 minutes so they were warm, didn't want to take them up too far). The porpoising diminished with the extra tire pressure, but certainly didn't go away. I'll look into the shocks, I'd been thinking that they may be the culprit. The truck has about 86k on it, so I wouldn't think that the shocks would be in bad shape, but you never know what the PO of the truck might have been dragging around.

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Ben - FL
Admiral

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880 Posts

Response Posted - 09/10/2006 : 13:43:35

If the stem is not all the way snug up against the bow bumper on the trailer is will bounce badly. I had to suffer this when I recovered Chick-a-pea once and there was just not enough ramp to get her the last four inches onto the trailer. The next day I refloated her at another ramp I knew had some depth to it and cinched her up tight to the bow bumper and the problem went away.

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Turk
Admiral

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USA
736 Posts

Response Posted - 09/10/2006 : 21:31:25

Hmmmmmm, never thought about the shocks. That sounds like a very good possibility. A 250 is a pretty beefy piece of equipment, if the trailer is level, it has to be the shocks. Probably worth changing anyway after 86K.

Good call Arlyn.

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CaptRon400
1st Mate

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USA
90 Posts

Response Posted - 09/13/2006 : 08:01:04

You've got to measure the tongue weight before you do anything else. It sounds like you do not have enough. It should be in the 500 to 600 pound range. You can use a bathroom scale with a 4 foot 2x4 and some short 2x4 blocks. Put the scale under one end of the beam, some blocks on the other and the hitch 1 foot from the blocked end. Whatever it reads should be multiplied by 4.

You can move the axles forward or aft on most trailers to compensate for any problems above. An equalizing / sway control hitch can really help, but try to get the tongue weight right first.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.