Reply
 
Thread Tools Search this Thread
 
Old 21 June 2006, 15:53   #1
Member
 
Nasher's Avatar
 
Country: Other
Town: Principalite d'Chaos
Boat name: The Nashers Revenge!
Make: Ocean & Bombard
Length: 6m +
Engine: Suzi DT200EFI, DT9.9
MMSI: "Mmmmm SI" she said!
Join Date: Jan 2004
Posts: 4,147
Engine support.

Iíve been spending a lot of time and effort on my trailer lately, itís now sprouted twin matching axles, bearing savers etc.

Even though I know its not good practice, Iíve always towed it around with the engine just raised up part way on the hydraulics.

Thinking about it, whether its on a lump of wood inserted between the saddle and engine, or just on the hydraulics, the forces involved as 200kgs of engine wobble about are all transferred to the transom through the relatively small area of the saddle, which I know happens anyway when bouncing about over the waves.

So Iíve considered making up a ĎYí bracket that braces the gearcase to the trailer, but Iím not happy that any movement of the boat on the trailer will transfer unacceptable forces through the gearcase and hydraulics.

So Iím considering putting some pads and eyes near the bottom of the transom that will take the feet of a small ĎAí frame, the apex of which will then strap to the gearcase via a rubber block. Iíd attach the frame to the eyes and power the engine down onto it.

Question is, by locking it all up solid, am I going to be putting undue stress on the area of the gearcase that touches the rubber block?
The hydraulics at least act as a shock absorber.
Any other comments?

Nasher.
__________________

__________________
RIBBED For extra pleasure.
Member of the ebay Blue RIB cover club.
Member of the Bombard 380 Aerotec club
Nasher is offline   Reply With Quote
Old 21 June 2006, 16:05   #2
Member
 
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,194
engine up

what i do is to raise the engine fully then down on to its engine stop, get a small say 500 kg ratchet strap and connect it to the towing eye on the transom, then around the engine, mid section then to the other towing eye, do it relatively tight, that will take the stress off the hyd's,
__________________

__________________
matt h is offline   Reply With Quote
Old 21 June 2006, 16:15   #3
Member
 
Nasher's Avatar
 
Country: Other
Town: Principalite d'Chaos
Boat name: The Nashers Revenge!
Make: Ocean & Bombard
Length: 6m +
Engine: Suzi DT200EFI, DT9.9
MMSI: "Mmmmm SI" she said!
Join Date: Jan 2004
Posts: 4,147
The drop down stop should not be used for towing. and anyway if I use mine the engine is almost horizontal.

The saddle and small area of transom are still taking all the bending forces though. I'm trying to spread the load over a bigger area.

Nasher.
__________________
RIBBED For extra pleasure.
Member of the ebay Blue RIB cover club.
Member of the Bombard 380 Aerotec club
Nasher is offline   Reply With Quote
Old 21 June 2006, 16:16   #4
Member
 
Country: UK - England
Town: solent
Boat name: wilson
Make: jeanneau merryfisher
Length: 5m +
Engine: suzuki df 70hp
Join Date: May 2006
Posts: 70
it dosnt seem that this would acheive much, the weight now is on the transom spread quite well with the engine,transom and trailor rubbers absorbing pressure
your suggestion with an a frame on the transom,puts opposing forces on the transom,and gearcase.the rubber absorbing little i suspect it would stiffen everything up too much?
the a frame also puts a higher pressure in another direction on the transom which it is not built for this could act as a swinging pressure motion weakening the transom further
im no expect but save your money and time would be my advice
__________________
antiqueboy is offline   Reply With Quote
Old 21 June 2006, 19:50   #5
Member
 
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,653
The reason for supporting the motor while trailering is to minimize the pendulum effect and subsequent wear on the hydraulics and the transom.

While you're in the water and running, the force on the transom is generated from the prop. It is usually in a forward direction, with some twisting force from the arm created by the distance from the mounting bolts to the prop. In any case, while the forces can be fairly substantial, I think they are a much more gradual type force than the bouncing you get while trailering.

Most of the "transom savers" or "motor support brackets" I've seen have the lower unit supported in a block of some sort, and the bracket ties in to the trailer in some fashion (often to the rear-most keel roller or to a bracket on the rear crossmember.)

What this does is two-fold: It minimizes any kind of rocking action on the motor and its pivot points, and it transfers some of what does occur to the trailer itself, rather than channeling it all into the transom.

There are other methods (which I am skeptical about, at best): some people use a "M-Y Wedge", which is a small plastic tube, for lack of a better description, that slips over the shaft on the trim ram, thus taking the strain off the hydraulics; others use a piece of lumber placed between the motor and the mount, and relieve strain that way. Neither of these address the pendulum forces that the motor experiences as you go over bumps and what-not.

If you want to go with a quick and easy (note I didn't say "cheap") solution, take a look here:

http://www.swivleze.com/prod_ts.ht

jky
__________________
jyasaki is offline   Reply With Quote
Old 21 June 2006, 20:09   #6
Member
 
Country: UK - England
Town: Towcester
Boat name: Treliska
Make: Ribcraft
Length: 6m +
Engine: Outboard 225 Optimax
MMSI: 232009522
Join Date: Feb 2006
Posts: 187
RIBase
Does anyone actually know where the centre of mass is for a large (150hp say) outboard? I started drawing a free body digram for this to take a look at the forces in a support, and then realised that i didn't have a clue. If you pick up a small outobard, the CoM is almost in the engine block, but i don't have a clue how that changes as the engine gets bigger.
__________________
Andy_Rs600 is offline   Reply With Quote
Old 21 June 2006, 20:59   #7
Member
 
Country: Other
Town: San Carlos, Mexico
Boat name: INDE
Make: LOMAC 730
Length: 7m +
Engine: 200 Merc.
MMSI: Please press 1
Join Date: May 2006
Posts: 1,688
Send a message via Skype™ to Limey Linda
Don't make it too complicated. The effective center of mass is the centerline of the centerline of the horizonal engine pivot. That is where the load is taken regardless of tilt angle. This pivot point is typical 12 " aft of the transom. Using hydraulics to secure the engine is a bad idea; after a few bumps you will force the oil back though the cylinder valves and it will become sloppy. Using the lift catch is a really bad idea. The old trick of lowering the engine on a piece of wood and then using a heavy duty bungee to strap the skeg to the trailer, this will stop upward/downward motion and compensate for small movements of boat on trailer: really works. Unless your driving a dragster all boat movement will be forward due to braking so make sure it is a good strong bungee Remember it is the bouncing that does the damage not the weight. Ever gone over a speed bump ( sleeping policeman , as I remember) too fast and felt your arse lift off the car seat????? and your in the vehicle. Imagine what is happening to your engine which is pivoted off the back maybe 25-30 feet feet away. Your arse moves up/down a little but your engine wants to move one hell of a lot more.

Hope this helps. T.
__________________
Running around like a head with it's chicken cut off.
Limey Linda is offline   Reply With Quote
Old 22 June 2006, 04:17   #8
Member
 
Country: UK - England
Town: Towcester
Boat name: Treliska
Make: Ribcraft
Length: 6m +
Engine: Outboard 225 Optimax
MMSI: 232009522
Join Date: Feb 2006
Posts: 187
RIBase
Quote:
Originally Posted by Limey Linda
The effective center of mass is the centerline of the centerline of the horizonal engine pivot. That is where the load is taken regardless of tilt angle. This pivot point is typical 12 " aft of the transom.
my little brain doesn't understand........

The load is always applied in the same place as long as there is only one support. In that case the posiion of the CoM only affects the moments(bending loads) applied to that support. If there are 2 supports that changes. The distribution of forces and moments between the supports depends totally on the position of the CoM.

As it is probably the bending moments that do most of the damage to the transome, the ideal support would provide enough stiffness to rotation of the engine that the transome bracket did not have to carry much bending load. Alternativly, you could make the normal mounting floppy enough that it didn't carry load, but that would probably involve bleeding the hydrualics. There are a few simple ways of making the joint between transome and support (or trailer and support) such that it can not transfere any bending load to the boat/trailer either. If this were all set up right, the only loads the transome would have to take (almost) would be pure compression. Being as fiberglass is stiff in compression, there isn't much fatigue action associated with that loading, so you're boat doesn't break
__________________
Andy_Rs600 is offline   Reply With Quote
Old 22 June 2006, 06:51   #9
Member
 
Country: UK - England
Town: Crawley,West Sussex
Boat name: Droopy 2
Make: Avon Searider
Length: 5m +
Engine: Tohatsu 90hp
Join Date: Feb 2006
Posts: 39
Engine support

Started something there didn't you Nasher !!
__________________
25% of a whale circumcision team - FOUR SKIN DIVERS!!
DavyBuoy is offline   Reply With Quote
Old 22 June 2006, 18:45   #10
Member
 
Country: Other
Town: San Carlos, Mexico
Boat name: INDE
Make: LOMAC 730
Length: 7m +
Engine: 200 Merc.
MMSI: Please press 1
Join Date: May 2006
Posts: 1,688
Send a message via Skype™ to Limey Linda
http://www.m-ywedge.com/ This is new and makes sense to me. I would still use a heavy bungee to stop upward movement. If you get one let us know how it turns out. Watch the demo video.
__________________

__________________
Running around like a head with it's chicken cut off.
Limey Linda is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 18:30.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.