Interesting, a Catalina 22 is exactly what I had in mind when considering
the largest towable boat! Good to hear your experiences. I've been really
looking for a com-pac 19, but there aren't that many out there. Com-pac 23
would be ideal, but is getting too heavy and difficult to trailer in
general. However, if a nice Catalina 22 for a good price comes around, I
might just jump on it!
Jaime
On Wed, Oct 14, 2009 at 5:22 PM, tyler <casi...@usermail.com> wrote:
> Jamie,
>
> I'm also towing a sailboat ('74 Catalina 22)- I highly recommend one as
> it's cheap and very well made. It only weighs about 2200lbs, but the trailer
> and gear bring it to about 3500. I'm currently towing it with a beat up '87
> Volvo 740 turbo wagon that tows it very well, but I think the W124 would be
> more comfortable and fuel efficient. I am also curious also about the
> Mercedes' ability to pull up a ramp. The Volvo has been able to pull the
> boat up even the steepest of ramps without issues. It has an automatic with
> 2.45:1 1st gear, and a 3.73:1 rear axle with an Eaton G80 locker- and the
> engine makes 187 ft*lb (253 Nm) of torque at 2900 rpm. Does anyone have the
> gear ratio and torque specs for the W124? Is it available with a locking or
> limited slip rear differential? I would assume if it has just as low or
> lower gears, a locker or LSD, and as much torque then climbing the ramp
> shouldn't be an issue.
>
> I am mostly worried about the transmission or brakes in the W124 burning up
> going over mountains.
>
> For pulling up a ramp, I think one could calculate reasonably well the
> steepest ramp you could pull a given boat up given (1) the torque of the
> engine at the stall speed of the torque converter, (2) the ratio of 1st gear
> times the rear differential, (3) the tire outside diameter, and (4) the
> combined weight of the entire rig. It's #1 that I expect to be hardest to
> find...
>
> Searching online, I found that my Volvo has a 2700rpm stall speed torque
> converter and makes about 175 ft*lb of torque at this rpm - or about 1599
> ft*lb at the rear axle. With a 12.5in tire radius, this is about 1535 lbs of
> forward thrust. Fully loaded will all of my gear, the car and boat probably
> weigh 7,000lbs.
>
> So:
> Force = weight * sin(ramp angle)
> ramp angle = arcsin(force/weight) = 0.22 radians = 12.61 degrees
>
> So in theory I can probably pull up a 12.61 degree ramp. According to
> BoatUS, most ramps are designed for a 6:1 slope (arctan(1/6)=9.46 degrees),
> so I have a good extra margin of ability, although without a locking diff
> traction would probably come into play first. If someone can help me find
> those same numbers for the W124 300TD, I will redo the calculation for it.
>
> Tyler
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