Determining Shaft length on a Zodiac FC470 - Page 2

twtrk1 · 27 July 2013, 00:26

Mercury makes a short shaft 40hp. That is the only motor I was able to find new. I also found a guy that would make a bolt-on transom riser for a longer shaft motor

SIBRider · 29 July 2013, 15:50

How low below keel does anti-cavition plate should be on F470 at transom? My transom is 18". Common wisdom is 0-1" below on regular boats. That puts motor quite a bit above transom. Should anti-cavitiona plate be lower on F470 because of speed tubes?

captnjack · 30 July 2013, 17:47

Quote:

Originally Posted by SIBRider

How low below keel does anti-cavition plate should be on F470 at transom? My transom is 18". Common wisdom is 0-1" below on regular boats. That puts motor quite a bit above transom. Should anti-cavitiona plate be lower on F470 because of speed tubes?

20" shaft.
The wisdom is supposedly that the deeper prop (and deeper exhaust) will be quieter for your commando beach landings...

After trying it, you might consider a small black of wood under the motor mounts to raise the engine an inch or two. You might get a little more speed with less splashing.

SIBRider · 30 July 2013, 17:51

So is it an inch or two? I'm thinking to bolt motor down. Don't want to drill too many holes.

F470 · 24 March 2014, 02:20

So I ended up replacing the short shaft with a long shaft (or extra long shaft, can't quite tell) Suzuki DT-40. The DT-40 sits about 4.75" below the keel. I've noticed excessive splashing and fuel consumption. Do I need a Transom Riser?

F470 · 26 June 2014, 20:39

I have decided to design and fabricate a transom riser. So what is the optimal location for the cavity plate on a Zodiac F/FC-470? Is it exactly flush with the keel or is it 1/2 - 1" below? If it is exactly flush will I have issues with loosing traction when there's a lot of waves? I have drawn up a design in CAD. I am contemplating making it adjustable but I don't know if it is necessary. On the other hand I don't know what the sweet spot is. Currently I need to move the transom up about 4.75" in order to make the cavity plate flush with the heel. Should I make it flush or set it slightly below?

SIBRider · 26 June 2014, 21:04

Quote:

Originally Posted by F470

I have decided to design and fabricate a transom riser. So what is the optimal location for the cavity plate on a Zodiac F/FC-470? Is it exactly flush with the keel or is it 1/2 - 1" below? If it is exactly flush will I have issues with loosing traction when there's a lot of waves? I have drawn up a design in CAD. I am contemplating making it adjustable but I don't know if it is necessary. On the other hand I don't know what the sweet spot is. Currently I need to move the transom up about 4.75" in order to make the cavity plate flush with the heel. Should I make it flush or set it slightly below?

Good idea! I've been happy at 1/2" below. Only experiment would tell for sure but I think Raising it 4"+ makes such a massive difference that last 1/2" wouldn't matter nearly as much. Adjustable would be nice at least for experiment. Does your motor have number of mounting holes? It may allow to mount at meaningful height. If you keep your 1/2 sacrificial plate make sure clamps can grip such thick transom. Mine would not. I only have at best 1/4 of threads left after clamping over transom + 1/4 alum plate x2

F470 · 26 June 2014, 21:16

The motor only has one pair of mounting holes but the idea was that by switching out the insert inside the transom riser I could adjust the angle. I plan to remove the sacrificial plate and the aluminum motor mount pad but keep the aluminum bar I have on top of the transom. The yellow parts are two rubber pads that I would use to shim the remaining space. I will definitely check to make sure its not too thick. Thanks!

SIBRider · 26 June 2014, 21:39

I wouldn't use anything compressible. HDPE maybe. One problem I can see is matching standard rectangular pipe stock usually 1.5" or 2" to something lapping 40mm transom + thickness of pads. Guess you could shim 1.5 rectangular with with 1/8-1/4 plate.

I doubt you would adjust it much later. In my case I just cut three 1/2" HDPE plates of desired width + one extra of needed thickness on table saw.
If riser is too tall (unlikely) you can always just cut those down.

F470 · 26 June 2014, 22:40

I think I'll skip the adjustability aspect. In the unlikely event I can always as you say trim it later.

SIBRider · 26 June 2014, 23:00

another suggestion would be to use same bolt pattern as you motor to mount raiser. Imagine it mounted as high as possible. Then you always loose raiser if need to and use those holes to attach motor still possibly considerably higher than simply dropped on transom. I would certainly use 4 bolts for riser.

F470 · 27 June 2014, 00:00

Yep. I plan to use the same bolt pattern as the engine mount and two additional ones. Not sure I understand what you meant past that first sentence...

SIBRider · 27 June 2014, 00:19

Quote:

Originally Posted by F470

Yep. I plan to use the same bolt pattern as the engine mount and two additional ones. Not sure I understand what you meant past that first sentence...

What I mean is you can drill pattern corresponding to lowest position of motor. Place motor squarely on transom and drill using bolt holes as guides.

Alternatively you can raise motor with wood block or something and again use bolt holes as guides for drilling. But then I would keep distance from top holes to top of transom not much less than thickness of transom. i.e 40 mm.

F470 · 27 June 2014, 20:50

I updated the design. Made it 0.25" aluminum with 2" x 4" rectangular extrusion inside. I also added the Motor clamp to get an idea of layout and position. 4 additional holes to secure the riser for a total of 6. This raises the motor 4.25" so that the cav plate sits 0.5" below keel.

SIBRider · 27 June 2014, 23:13

Quote:

Originally Posted by F470

I updated the design. Made it 0.25" aluminum with 2" x 4" rectangular extrusion inside. I also added the Motor clamp to get an idea of layout and position. 4 additional holes to secure the riser for a total of 6. This raises the motor 4.25" so that the cav plate sits 0.5" below keel.

Do you clamps fit 2.5"? Are you sure you need to got that high? Are you trying to match distance from bracket to A/V plate (22.75") or is it actual measurement of ? When you trim out your motor AV plate may go up by an inch or so relative to keel at neutral trim.

F470 · 27 June 2014, 23:23

The clamps should fit as the opening is closer to 2.75" but I will of course double check to make sure. I'm not sure if I have the height dimensions correct. As currently measured the cav plate is 4.75" below the keel. From the top of the transom to the top edge of the riser plate its 4.25". That's how I got here. Are my calculations off? I'm new to all this so I am a bit slow to follow. What do you mean 'trim out the motor AV plate'? Which one is the AV plate?

SIBRider · 27 June 2014, 23:33

Quote:

Originally Posted by F470

The clamps should fit as the opening is closer to 2.75" but I will of course double check to make sure. I'm not sure if I have the height dimensions correct. As currently measured the cav plate is 4.75" below the keel. From the top of the transom to the top edge of the riser plate its 4.25". That's how I got here. Are my calculations off? I'm new to all this so I am a bit slow to follow. What do you mean 'trim out the motor AV plate'? Which one is the AV plate?

ah. AV plate is one above prop. Comma might help.
When you trim out your motor, AV plate may go up by an inch or so relative to keel at neutral trim.

SIBRider · 27 June 2014, 23:37

neutral trim as when boat is on a plane, AV plate should be near horizontal.

F470 · 28 June 2014, 00:26

So you're saying that at neutral trim (meaning boat is on a plane?) the AV (Anti Cavitation) Plate may rise an inch? So in that even I should probably reduce the overall height of the riser plate by 1"?

SIBRider · 28 June 2014, 02:42

Yes but you have to measure it mounted to be 100% sure