Help get my boat running true!

[Frank Acampora]

Re: Help get my boat running true!

Well, back to props: Understand that I threw out a 21 pitch stainless based on what I am running or did run on the 90 and 125. ULTIMATELY, the test is what RPM your engine is running. If you are now turning 5000 to 5500 RPM with a 19 pitch aluminum prop then the 21 stainless should give the same RPM at a couple of MPH faster. You are using a tach, aren't you? It is the most important gauge on your boat and if you don't have one, that should be your first priority

The attitude of your "cav" plate may be due to the angle of your transom. It it ( the transom) is relatively vertical then you won't be able to get much "tuck-in"

If teh angle of the plate is not the problem, then put a level or good straightedge on the bottom of the hull. "Rocker" can cause porpoising.

You will also be MUCH happier if you spend a couple of hundred on a 2 to 1 lower unit. I do not believe that the 115 had 2 to1. You can check by turning the flywheel by hand in gear. Two turns of the flywheel will give either one turn of the prop or about 1 1/4 turns. If it is 1 1/4, then the ratio is 1.76 to 1. The 2 to 1 lower is faster by about 4-5 MPH.

Again, it all depends upon how serious you are about getting maximum performance out of your combo.


A couple of better photos (side and rear view) with the engine down and tach readings when you get it running correctly would be very helpful. Your low speed problems MAY be due to incorrect idle speed. Go back to the Force forum and read the sticky on synchronizing carbs and timing.

 

[Willyclay]

Re: Help get my boat running true!

Double post, but...just went out to test to see if i could get it to tilt down any further to make the cav. plate any flatter. But i found that the way i have it at the moment, is as flat as i can get it. So not sure what's causing it. But if i havent been able to get it trimmed out flat when im running then possibly another cause of my symptoms?

Would a pair of transom wedges help?

http://www.iboats.com/Transom-Wedge/dm/*******.031992398--session_id.958962002--view_id.40151

 

[Andy'sDelight]

Re: Help get my boat running true!

Your friend's boat, in addition to having a hydrofoil on the motor, also has a deep-v hull and a motor that is matched to the transom height. Your motor is a long-shaft model on a short-height transomed boat that has a flat, racey hull with mini-tunnels and non-trip chines. While Smart-Tabs probably will help, an adjustable jack-plate might be the ticket instead of that fabricated transom extender. Finally, your motor does not appear to have PT&T which may be the single most helpful method of controlling bowrise and porposing. Good luck!

EDIT: The link below will let you see diagrams of what Mercury says about mounting height.

http://continuouswave.com/whaler/reference/engineMountingHeight.html

Everything Willy said is dead on. Your friend's boat is worlds different than yours. The bow rise is minimal. The porpoising certainly would annoy me and probably would knock some fillings out. Power trim and tilt would probably solve your issues. Without it your only solution would be tabs. Not sure Smart tabs would help with the porpoising as much as they are pretty much fully retracted at speed.

 

[Willyclay]

Re: Help get my boat running true!

The motor has the hydraulic tilt control on it, but it seems to get a little slow at the end of the travel and almost strain against itself to pull into a full upwards/downward position.

Maybe your "hydraulic tilt control" is like my 1968 Johnson 100HP which is tilt only and has zero trim capability at speed. Good luck!

 

[Sabbath]

Re: Help get my boat running true!

Well, back to props: Understand that I threw out a 21 pitch stainless based on what I am running or did run on the 90 and 125. ULTIMATELY, the test is what RPM your engine is running. If you are now turning 5000 to 5500 RPM with a 19 pitch aluminum prop then the 21 stainless should give the same RPM at a couple of MPH faster. You are using a tach, aren't you? It is the most important gauge on your boat and if you don't have one, that should be your first priority

The attitude of your "cav" plate may be due to the angle of your transom. It it ( the transom) is relatively vertical then you won't be able to get much "tuck-in"

If teh angle of the plate is not the problem, then put a level or good straightedge on the bottom of the hull. "Rocker" can cause porpoising.

You will also be MUCH happier if you spend a couple of hundred on a 2 to 1 lower unit. I do not believe that the 115 had 2 to1. You can check by turning the flywheel by hand in gear. Two turns of the flywheel will give either one turn of the prop or about 1 1/4 turns. If it is 1 1/4, then the ratio is 1.76 to 1. The 2 to 1 lower is faster by about 4-5 MPH.

Again, it all depends upon how serious you are about getting maximum performance out of your combo.


A couple of better photos (side and rear view) with the engine down and tach readings when you get it running correctly would be very helpful. Your low speed problems MAY be due to incorrect idle speed. Go back to the Force forum and read the sticky on synchronizing carbs and timing.

When i first got the boat, some of the gauges werent working, so i pulled them out. I've since cleaned the shed, and cant find some of them at the moment (doh) which is a shame because they were nice retro looking gauges to suit the boat.

Just went out and had another look at the boat. The motor tucks in by a couple of degree's. So the motor is going all the way down, and it's trimming in to the point where the straight edge eventually intersects with the bottom of the hull when placed against the bottom of the cav plate.

This i believe is what you want to get up on plane quicker? And then trim it up a couple of degrees? Because i wasnt touching my trim at all while the boat was running and was running it trimmed in all the way the entire trip.

Everything Willy said is dead on. Your friend's boat is worlds different than yours. The bow rise is minimal. The porpoising certainly would annoy me and probably would knock some fillings out. Power trim and tilt would probably solve your issues. Without it your only solution would be tabs. Not sure Smart tabs would help with the porpoising as much as they are pretty much fully retracted at speed.

At the end of this video, it gives a comparison shot between tabs and no tabs, and the porpoising seems definately decreased. Or are you saying it's not going to do what the video says?


But i've also seen video's for "Stingray Stealth" Hydrofoils which claim the porpoising is reduced etc. I just want to get something for now that will cut out the porpoising atleast a little bit. I could go to the shop tomorrow and buy a hydrofoil for ~$100. But i dont want to then stick it on and find it's doing bugger all for the problem when a set of ~$180 Smart Tabs would have done better.

With the running issue i do intend on trying again to reset the carbs. I spent 2 days out on the lake trying to get it going into gear without cutting out. And now it's there and im scared of touching anything incase it starts being problematic again

Maybe your "hydraulic tilt control" is like my 1968 Johnson 100HP which is tilt only and has zero trim capability at speed. Good luck!

Sounds like it, although i think i've got the reasoning it goes so slow at the base of the run sorted out.

*Sigh* This problem

 

[Sabbath]

Re: Help get my boat running true!

Weekend's here. Time to get some pictures.