Outboard mounting angle

[hardwater fisherman]

I have a new to me boat that I installed my long shaft 1976 40 hp evinrude on. It is a 16 foot fiberglass tiller with an almost flat bottom with rounded sides and a deep V bow. It is 68 inches wide at the transom and 74 inches at its widest point. It is rated for 45hp and for 1580 lbs capacity. The transom measures 20 and 1/2 inches. The transom has less of an angle from the runabout the motor came off of. Therefore the prop is closer to the transom. I get the best performance from running the tilt pin in the top hole. And it will run in the third hole but I lose speed and the boat digs in at higher speeds. I blocked the motor up as high as possible and I gained a little speed but still needed to run in the top hole. I am okay with the speed of 27 mph but it feels and looks odd with the motor tilted like it is, I thought about shimming the motor to set it back or maybe setting it back with a manual jackplate. Even with motor propped up 3/4 of an inch the anti cav plate is almost 1 inch below the hull. The old boat I had was above the bottom of the hull and I ran in the 2nd or 3rd hole. If anybody has any ideas or comments I would like to hear them. THANKS.

 

[Cat nip]

Have a picture? If it's a bolt on motor try raising it up that way.

 

[hardwater fisherman]

I dont have a picture of the back at the moment. And it is held on by the clamp screws and not bolted. I have drilled holes in the very bottom of the stern bracket. But there would be nothing holding on top if I were to raise it any higher. It is of the same style as the 1950s and quite limited for performance. EDIT The boat it came off of I rebuilt the transom. And I made it around 22 inches. But as I said the transom had a much different angle. I think that would be too high on this boat.

 

[Sea Rider]

Any OB has sufficient trim holes (angles) for OB to sit perpendicular (90°) to water level, that's the position for best prop thrust. Raise, lower OB, whatever need to do for water flow at speed to skim right unde small upper water splash plate when combo is on plane provided that deck load is evenly distribited.

Once the sweet OB/transom height has been fully reached, with an induction tach installed go for a prop maximization to a less pitch prop to pull wot revs up between middle if wanting better top end speed or full wot rpm if wanting best top hole shot as usually loaded, you decide.

Post a sideway pic of the lower tail while OB sits on transom with combo out of water if possible.

Happy Boating

 

[hardwater fisherman]

As I said this motor is very limited. There were only 4 props made for it and I have 2 of them.The only one to be had new now is 10 3/4 x 11. Which I already have. And these props are not a modern design. And if I trim the motor 90 degrees to the water line that would be in the second hole. The boat plows through the water when ran below the third hole. To make the plate even with the hull I would need to raise the motor 2 inchs. And there is not enough transom. I had my last boat set up as you describe but it is because I built the transom higher. I suppose I will have to build a transom riser to see if I can the motor tucked in a little more. Also because the main cooling water intake is attached to the underside of the anti cav plate and just above the prop. I assume it was designed to run little deeper than a motor with the water pickups lower down on the sides.

 

[racerone]

Make some wedges to change the transom angle.

 

[hardwater fisherman]

Thanks I asked about that in post#1 but I said shims instead of wedges. This might be a stupid question but I am thinking the thicker part of the wedge will be on top?

 

[racerone]

The common / most popular transom angle is 12 degrees.-----Measured yours ?

 

[hardwater fisherman]

I used a formula I found and it measured 13 degrees. So probably not far off from normal.

 

[Sea Rider]

You can compensate OB 90° angle difference by shifting weight/load aft or forward if needed if wanting OB to ride at perfect 90° when combo is on plane. But won't gain much if OB does not sit at the sweet transom height spot for lower leg to achieve the least water drag along top prop thrust.

Happy Boating.

 

[hardwater fisherman]

I think I was able to get the most out of my motor. I raised the transom 1 1/2 inches and moved two batteries about 3 feet forward. Yesterday with my girlfriend and her grandson, a heavy cooler. Probably around 180 extra pounds. I was able to get up to 28 mph and it plane out nicely. Also the lake was a little rough and there was a fairly strong wind. So a test with just me and a calm lake will be next. But it looks promising. THANKS all.

 

[82rude]

You have a pin drive motor.Props are limited now.I have a mechanical variable ratio prop off of a 1956 30 hp Johnson that I use for dialing in what prop I need.The beauty of omc was you had the same props for many years and many hp ratings on the smaller motors.28hp,33,30,35,40,pin drives .I will post a pick for those that would like to see it.

 

[82rude]

Goes from 10p to 19p.

 

[hardwater fisherman]

Yes the second prop I use is from a 1963 28hp. It gives a better hole shot and less top speed. So when I have a heavy load I use it. That is an interesting prop you have.

 

[jimmbo]

You have a pin drive motor.Props are limited now.I have a mechanical variable ratio prop off of a 1956 30 hp Johnson that I use for dialing in what prop I need.The beauty of omc was you had the same props for many years and many hp ratings on the smaller motors.28hp,33,30,35,40,pin drives .I will post a pick for those that would like to see it.

I have only seen pics of the prop, but have never had one in my hands. I am curious as to how it compares with the fixed pitch props?

 

[82rude]

I only us it to get the right pitch.I did use it one time with a 33hp and it seemed ok.

 

[Cat nip]

I wish i had known of those adjustable props when i was running twin big twin 35's in a 1953 16' alumacraft, they ran out of prop at about 45mph with 15 pitch props lol.