RPM/Engine Height/Prop Questions

[100333624]

OK, it's a 2 stroke 115 HP Yam.

Need some information about last pic posted data :
- At which trim position were you when water flow passed right under upper plate, trimmed down, middle, trimmed up ?
- Was load well distributed on deck to achieve a well balance combo.
- How much under upper plate was water flow at speed passing bye ?
- How did you check the posted height while water flow was passing through lower leg.
- Popped you head out transom, installed a go pro cam on transom facing downwards, someone was having g a look from other boat ?

Happy Boating

My trim gauge doesn't read properly, I trim it by feel. I am not sure exactly at what moment I looked over at it but I know I was trimmed out quite a bit at max throttle, told my partner to hold the wheel while I quickly stepped back to check. I can easily check it on my boat as long as I got someone to take the wheel. Load is distributed pretty good throughout the boat. I believe the upper plate was about an inch above the water surface and it was in the splash. It was pretty much where I would normally see the anti vent plate on others boats who've raised motors at the "optimum" height, which is just at or just above the water surface in the splash. I hope that answers your questions?

I will do a thorough test run tomorrow and will take some pictures possibly video too and post them for clarification.

 

[MARV1]

My anti vent plate is still buried under the water at speed though? Doesn't it cause more drag when buried, should I leave it like this?

Raise it one more hole. Ideal height is cavitation plate at or slightly above the waterline.

 

[100333624]

Raise it one more hole. Ideal height is cavitation plate at or slightly above the waterline.

Ya that's what my research shows, not sure if it'll make a huge difference on my hull but I'm willing to try it! Can't get it out for testing today as its too windy, seems like Sunday will be the next test run.

Are there any people with deep V center consoles on here who can report what they've found raising theirs? I can't be the only one.....

 

[Sea Rider]

You need to test your combo as suggested :

- Distribute load evenly on deck
- Trim engine at 0, perpendicular to water level
- Wot spin on flat calm, non windy water cond.
- Combo must ride parallel to water level when on plane.

You said that water flow at plane was passsing right under upper water delfector plate, as don't know by how much under your best engine/transom height will matching this example. Yam and Tohatsu engines likes to work spot on as shown on pic.



If it's slight under stay there if at say middle between both plates rise one hole or holes to achieve for water flow to skim right under WDP (yellow line) Non clamp engines are more difficult to height dial, going one hole up or down is about about 20 mm height difference as opposed to clamp engines in which you can play with engine heights by the milimeter raise if you need to.

If hydraulic steeering mechanism is working top, that's fluid is not leaking, steering shaft is well greased, the unwanted load on steering wheel could be due to engine being bady trimmed from, engine height issue, badly balanced deck or a combination of all 3.

In reality doesn't matter much for recreational boating if you have a flat, shallow, deep hull, what you need is match that hardened shaped water flow passing out transom right under WDP and that's playing tail heights. Patience, good disposition, water trials and looking what's happening out transom is the way to go.

Test as suggested and report back your findings....

Happy Boating

 

[100333624]

You need to test your combo as suggested :

- Distribute load evenly on deck
- Trim engine at 0, perpendicular to water level
- Wot spin on flat calm, non windy water cond.
- Combo must ride parallel to water level when on plane.

You said that water flow at plane was passsing right under upper water delfector plate, as don't know by how much under your best engine/transom height will matching this example. Yam and Tohatsu engines likes to work spot on as shown on pic.



If it's slight under stay there if at say middle between both plates rise one hole or holes to achieve for water flow to skim right under WDP (yellow line) Non clamp engines are more difficult to height dial, going one hole up or down is about about 20 mm height difference as opposed to clamp engines in which you can play with engine heights by the milimeter raise if you need to.

If hydraulic steeering mechanism is working top, that's fluid is not leaking, steering shaft is well greased, the unwanted load on steering wheel could be due to engine being bady trimmed from, engine height issue, badly balanced deck or a combination of all 3.

In reality doesn't matter much for recreational boating if you have a flat, shallow, deep hull, what you need is match that hardened shaped water flow passing out transom right under WDP and that's playing tail heights. Patience, good disposition, water trials and looking what's happening out transom is the way to go.

Test as suggested and report back your findings....

Happy Boating

Sorry it took a few days but I finally ran another test today, unfortunately I couldn't snap photos but I did take a GOOD look at what's going on. I did a few runs at WOT and I noticed that at 5500 rpm I was maybe just a tad trimmed too much out and could hear the prop cavitating? Started sounding more like a deep V6 sound, and didn't change speed only raised rpm slightly. Seems like 5400 rpm is the sweetspot and runs 77 kph, still has decent amount of bite in the water.

So when I jumped in the back to check out the splash, my anti vent plate was just kindof on the surface of the water, I could see the top of it and it was in some heavy splash, but I could easily make out the top of the plate. I think it could probably come up one more hole but I think I'm going to keep it this way, I kind of like the feel of it. I did get a little cavitation on tight turns but nothing I can't fix with a very minor touch of the trim button.

As for the V splashing, it's the water coming up and hitting the bottom of that WD plate and being redirected on both sides of the lower unit. I noticed if I wasn't trimmed parallel to the water surface, the V splash was kind of on an angle going up (back) away from the boat, but when trimmed parallel it was level with the surface throwing it back but level, not on an upward angle.

The steering torque wasn't as bad this time, if anything it felt normal as with any other prop I tried. I think the last run I trimmed way too much out which could be why my steering was so tight. I may try a 19" Laser 2 to get that rpm up just a little more, and if it over revs I will add some cup to make it grip better, I think this is the best bet so far.

Thanks all for your help and God Bless you all!

Nick

 

[Sea Rider]

Nick,

Some issues :

If WD Plate sits higher from water flow, it's normal to see flow climbing through sharp edge angle of atack, hitting under WD plate and re directing small splash to both edge sides. If WD plate skims right under water flow, flow will pass smooth flat unnoticed.

As in this example, once water flow engages right under WD, combo will plane faster due to prop having the right water bed amount of water under AV plate to grip properly and more efficiently achieving top thrust propulsion.




Besides best prop thrust and bite, combo will achieve excelent close turns at speed and overall good performance on any water cond.

To understand my suggestions, all the engine/transom height optimizations been doing for last 7 years were done on boats with non power trim Yam-Tohatsu engines, you'll be surprised on how fast combo is on plane provided that engine & prop are healthy, deck is evenly balanced while trim remains at a given fixed position that achieves combo riding parallel to water level.

Test again with the possibility to achieve the posted pic condition by playing with bracket's height holes.

Happy Boating

 

[100333624]

Nick,

Some issues :

If WD Plate sits higher from water flow, it's normal to see flow climbing through sharp edge angle of atack, hitting under WD plate and re directing small splash to both edge sides. If WD plate skims right under water flow, flow will pass smooth flat unnoticed.

As in this example, once water flow engages right under WD, combo will plane faster due to prop having the right water bed amount of water under AV plate to grip properly and more efficiently achieving top thrust propulsion.




Besides best prop thrust and bite, combo will achieve excelent close turns at speed and overall good performance on any water cond.

To understand my suggestions, all the engine/transom height optimizations been doing for last 7 years were done on boats with non power trim Yam-Tohatsu engines, you'll be surprised on how fast combo is on plane provided that engine & prop are healthy, deck is evenly balanced while trim remains at a given fixed position that achieves combo riding parallel to water level.

Test again with the possibility to achieve the posted pic condition by playing with bracket's height holes.

Happy Boating

Hi after further testing it seems this is the best height for me. Engine performs great, holds great even doing 45mph in 3' chop and it holds just beautifully! Will not change nothing other than might go with a 19" prop instead of the 20" and add some cup to it, it will be amazing. Thanks for your help.

 

[Sea Rider]

Nick,

Great to read it worked for you and anyone willing to try it out, just for the record, how close is water flow at speed passing by under WDP ? Once that cond is dialed while combo rides parallel to water level, both lower leg plates will achieve least drag compared to riding under or over trimmed. Have you had the opportunity to test close turns at speed on flat calm water, if so, were nicer that before, that's with least or non prop aeration whatsoever ?

Do you need to pull your current wot revs up a bit, assumed you were already there ? If max wot revs are already there or very close to it, going 2 pitches down will shoot revs up way higher than "rule of thumb" 300-400 + revs per 2 pitch decrease, so watch that out....

Thanks for posting your feed back.

Happy Boating