Wedge Between Motor And Transom - Why?

Chester

There are aluminum wedges between the Honda 40s and the transom. They are approximately 1/2" thick at the top and 1/16" at the bottom.
The only purpose seems to be to move the lower unit back a bit while under way. Can this be right? What am I missing?
Do other C-Dory's have this wedge?
Seeing how the boat is a tad stern heavy moving the motor forward even a bit appeals to me.

Rcbeach · Posted: Sat Jan 25, 2014 6:12 am Post subject:

Both C-Dorys I have purchased have had the wedges. My dealer says that the extra couple of degrees of engine tilt provided by the wedges gives a better ride in chop.

Sea Wolf

Sunbeam · Posted: Sat Jan 25, 2014 10:53 am Post subject:

I noticed on my boat that the engine seems to "like" to be trimmed all the way down (i.e. lower leg as forward as possible) most (all) of the time. If there were a wedge as described, then there would presumably be adjustment either way from that position, vs. now where it is at one extreme end of the range.

(This may change on my engine when I raise it slightly on the transom, but if not, or if it's "normal" for the C-Dory, then it fits with the idea of a wedge giving better/more usable trim adjustment.)

NORO LIM · Posted: Sat Jan 25, 2014 11:05 am Post subject:

There can be another trade-off with the wedges. Allowing the engine to tuck down further (thereby keeping the bow down) also means the engine will not tilt up as far. Depending on the tilt range of the motor, the mounting height of the motor, and the water line of the boat (especially when heavily loaded) the motor may not clear the water when tilted all the way up. This may not be a concern unless the boat is moored or anchored in the water a lot, and electrolosis, or marine growth fouling on the lower unit and prop are a problem.

With trim tabs, or Permatrims, and adjustments to mounting height the need or desirability of changing the transom angle may diminish or disappear. (Or even reverse, I suppose, i.e., at some point it might become beneficial to mount those wedges "upside down.")

Chester · Posted: Sat Jan 25, 2014 12:08 pm Post subject:

I've never run with the trim all the way down as it slows the boat considerably.
Get this, the boat came with the pin that limits how far down the motor can trim in the second hole from the bottom.

beermanPDX · Posted: Sat Jan 25, 2014 12:40 pm Post subject:

I really think the necessity would depend on the particular boat configuration. My boat also likes to have its motors trimmed all the way in (down), even with trim tabs in the equation. A 25 with twins, 3 batteries, and 23 gal of water all at the stern (not to mention the 100gal of fuel) is a VERY stern-heavy boat.

My boat doesn't have the wedge mentioned in this thread, but wonder if it should. I'm fighting a constant battle with a stern and engines that are too low in the water while running.

Lighthouse Express · Posted: Sat Jan 25, 2014 1:44 pm Post subject:

Ditto...

I can confirm beermanPDX findings since I have same configuration on my CD25.

Heinz

thataway · Posted: Sat Jan 25, 2014 2:42 pm Post subject:

I have never used transom wedges in any of the boats I have owned--including 3 conventional hull C Dories. It is rare that I trim the engine down all of the way. In some of the boats, I have found improved riding by adding the Permatrim, which seems to give more effect to the degree of trim. Only in the steepest of chop, have I wanted to trim the bow down. Usually by that time, I am running at a slower speed. Granted, the only twin engine C Dory I have owned is the Tom Cat 255.

If the boat requires wedges to run properly, I would consider that a negative or the two engines.

When cruising for a month at a time, our boats are heavy--with full tanks, extra 5 gallons of water, freezer, and ice chest in the cockpit.

The danger of running bow down too much is in down wind/down waves, there is the chance of both bow steering and broaching.

I have found, watching the fuel flow gauges, that the boats are most efficient in a relitatively neutral trim, to slightly bow down. Just my experience.

PeterQ · Posted: Sun Jan 26, 2014 1:41 pm Post subject:

The good folks at Mobile East Marine are proponents of the transom wedge, so of course there's one installed on my 25 (with single Honda 150) which you can see in my album.

This just alters the trim range available to provide a slightly more bow-down tilt range. Even with the engine trimmed all the way down, at 15 knots and nearly full fuel the deck angle is still a bit bow up, and just about right in 1-2 ft waves. In flat water and 25 knots, level trim is good. In heavy weather, I still need to slow way down and trim bow up to avoid the aforementioned broaching problem.

The Bennett trim tabs do help raise the stern some, but it may be that installing a Permatrim would improve the trim authority and do the most good. It's on my mod list and feedback from those of you who have them on the 25 would be welcome.

Sunbeam · Posted: Sun Jan 26, 2014 4:35 pm Post subject:

Chester · Posted: Sat May 24, 2014 11:09 pm Post subject:

Edit: The wedges are 1" thick at the top, not 1/2" as stated in my first post.
Update: I removed the wedges and raised the motors a notch.
The good. Now the anti-ventilation plates aren't submerged while planing which my research suggests is desirable. The engines gained 100-150 rpm at full throttle and can turn 6,000 rpm with 13" props.
The bad. There seems to be a bit more structure borne noise while under way, the props blow out with a modest amount of upward trim and vibrate when trimmed down. This yields a rather small amount of useful trim.
By making two changes at once it is hard to diagnose these issues.
The motors came with the pin that limits how far down the motor can trim in the second hole from the bottom. I still can't fathom how the wedges help because by lowering the trim pins to the lowest position trim is similar with said wedges removed.

thataway · Posted: Sun May 25, 2014 2:40 pm Post subject:

You are correct that the limit of the down trim may be adjusted, and if it was the same amount of trim down, is equal to the wedge, then why the wedge?

You want the anti ventilation plate just on the surface of the water (with the c Dory), not above it. This may be hard to achieve. I suspect that you are getting some ventilation on turns etc which is not desirable. I would drop the engine back down. I suspect that is the reason for the blow out, vibration etc….

I don't run with the bow trimmed all of the way down, except when trying to "cut" thru chop.. I try and trip for best RPM, at a given throttle setting. Of course the boats vary a lot because of the weight aboard, and the placement of this weight…

Thanks for the follow up post!

CAVU · Posted: Sun May 25, 2014 6:34 pm Post subject:

Chester,
I would guess that your boat was originally rigged by Sportcraft Marine in Portland, Or. My 2002 C-Dory 22 had the same wedges and it came from Sportcraft. You could argue whether or not they are necessary but from a practical standpoint the boat could still be trimmed in exactly the same manner with or without the wedges. The wedges would allow a little extra nose down trim from the engines, but when the motors are trimmed to a level position relative to the hull, it really makes no difference whether they are there or not.