Jack Plate for a 14ft V-bottom with Short Shaft Transom

[cchildr84]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Cchildr84

Can you post a pic of your 55 horse showing side of lower unit, cav plate, prop area to visually check your current lower leg shape.

Happy Boating

See pictures below of my 25HP. Like I mentioned in previous post, it's now just barely below the keel.

 

[Sea Rider]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Cchildr84,

Sit engine on top transom, with well ballanced boat, engine trimmed at 90? go for a wot spin, ideal engine transom height is for water flow skimming slightly under upper water deflector plate, forget all about anticav plate as this is a lower unit height optimization.

To understand, if water flow at speed hits the round edge, a water splash will be produced there, usually will have water jumping side of engine into deck, on the contrary water flow passing through sharp edge is mandatory to achieve best prop thrust.

If with time, be my guest, read this thread throughfully up to point 7.

http://forums.iboats.com/inflatables-ribs/abc-sib-rib-installation-guidelines-628902.html

Will have the overall installation idea more clearly. Although the thread was meant for Tohatsu engines, can be used as a quick guide for any brand portable engine installation.

Happy Boating

 

[cchildr84]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Cchildr84,

Sit engine on top transom, with well ballanced boat, engine trimmed at 90? go for a wot spin, ideal engine transom height is for water flow skimming slightly under upper water deflector plate, forget all about anticav plate as this is a lower unit height optimization.

To understand, if water flow at speed hits the round edge, a water splash will be produced there, usually will have water jumping side of engine into deck, on the contrary water flow passing through sharp edge is mandatory to achieve best prop thrust.

If with time, be my guest, read this thread throughfully up to point 7.

http://forums.iboats.com/inflatables-ribs/abc-sib-rib-installation-guidelines-628902.html

Will have the overall installation idea more clearly. Although the thread was meant for Tohatsu engines, can be used as a quick guide for any brand portable engine installation.

Happy Boating

Ok. With the information you've stated and the sketch up of the picture, I think I have things in their optimal position. The next time I'm out on the water I'll try and take a video and get a shot of the motor in the water at WOT w/o dropping my phone in the water. Haha. Thanks.

 

[kfa4303]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Here's a pic of a properly trimmed motor in action. Notice how the anti-vent plate is just breaking the surface of the water while at WOT.

 

[cchildr84]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Here a video of the boat running WOT. The av plate isn't quite visible, it matches more of the direction provided by Sea Rider. Like I say I think it's about as good as it going to get on this boat. I don't see the need to invest in a mini jack plate, I don't see that it's going to provide much if any benefit. Anyhow see the link to the video and let me know if you guys have any thoughts or comments. Thanks.

81 Evinrude 25HP at WOT - YouTube

 

[steelespike]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Do we know your rpm ay 27 mph? It seems to me you could get a little more speed with a 12" prop.
While it probably could go higher I don't think there is a need for it.

 

[steelespike]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Looks like the tinytach says about 5500 rpm? It seems like you could do a 12" prop and get a little more speed
Now I recall; your ratio is 1.75 And I think we discussed before assuming the tach is accurate your slip
is about 17% at 5500 and 27 mph.While a bit high; 12% is a more normal typical high normal
perhaps it's just an optimistic tach.

 

[Sea Rider]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

cchildr84

Looks fine to me, you have a clean undisturbed wake at rear engine. Is your engine sitting straight against transom, or you have a small shim under engine ? Seems you are top of max 5500 wot rpm for that engine, if so stay with that prop or you will be over rewing your engine with a less pitch prop if you happen liking going out lightly loaded.

Don't have anything against water flow passing skiming upper cav plate, the down issue is that on choppy seas or very close turns prop will lose thrust due to aereation issues, just good if going wot on straight non choppy sea runs.

Happy Boating

 

[cchildr84]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Looks like the tinytach says about 5500 rpm? It seems like you could do a 12" prop and get a little more speed
without killing hole shot too much. Do you know your gear ratio?

Im not sure of the gear ratio, I think earlier in this thread it was stated that these motors have a 1.75 gear ratio. I do have a 12" pitch prop, which I have not run wile by myself. I ran it with a friend in the boat and it wouldn't get past 5000RPM. Maybe the next time I go out by myself I'll put it on and see if I see any difference between it and the 11" pitch.

 

[cchildr84]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

cchildr84

Looks fine to me, you have a clean undisturbed wake at rear engine. Is your engine sitting straight against transom, or you have a small shim under engine ? Seems you are top of max 5500 wot rpm for that engine, if so stay with that prop or you will be over rewing your engine with a less pitch prop if you happen liking going out lightly loaded.

Don't have anything against water flow passing skiming upper cav plate, the down issue is that on choppy seas or very close turns prop will lose thrust due to aereation issues, just good if going wot on straight non choppy sea runs.

Happy Boating

I do not have the motor sitting against the transom top lip nor do I have a shim, I just have it tightly clamped to the upper portion of the transom. I check the tightness each time I go out to make sur the clamps haven't loosened.

 

[Sea Rider]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

So the engine rests on transom by its own weight, then you adjust clamps tight, right ? Place/glue a rubber pad on transom's inner metal plate, tight clamps to it, try to match both ears to face each other and secure with small rope, forget all about retightening clamps frequently.

Happy Boating

 

[steelespike]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

I believe the motor doesn't rest on the transom.It rests on a block to hold it at the height while tightening the clamps.
You need to be sure they stay tight as there is no margin for error.

 

[kfa4303]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

oops wrong post...

 

[Sea Rider]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

Cchildr84,

According to Steelespike you have a wooden shim between transom and engine, right ? The video shows a gap which assume is the wooden shim. If having a wooden shim, try to make another with just 50% of the actual shim height. According to the video you are about right regarding engine tail height, buy ideal would be for tail to go a tad lower, as to water flow at wot skimms slightly under upper water deflector plate. If 50% new wooden shim gives water splashes, you've passed the ideal WDP height, rise a tad.

I know testing under trial and error takes time, but once you have it correctly height dialed you will be pleased with the super performance you will achieve under all water conditions.

Boat takes sometime to fully plane, due to not having front weight, try moving best man's friend farthest to bow along gear to compensate weight distribution, full throttle, should plane faster. Post results if shiming tad lower, just for the record.

Happy Boating

 

[cchildr84]

Re: Jack Plate for a 14ft V-bottom with Short Shaft Transom

I think for this motor, where I have it will be sufficient. The only thing I'll try is to run the 12" pitch prop with just myself and see if that makes any difference. Other than that where I have it on the transom now will be sufficient for my needs. Thanks all.