Please dont be offrened, you have a good understanding of stuff..
Some of the questens/ statements below may seem well below your level of understanding...
There others reading who are interested in how things work.. so I consider them also.
OK looking at numbers
Put them all in the same place..
Senator RH620, set up to be 1300kg on the water
If correct and engine height correct you will have a WoT speed on flat water at best trim for THAT speed around 45 to 47 mph
I dont see a WoT speed above??
I would suggest the total gross weight would be greater than that.. maybe up around the 1800/1900 mark (???)
yam 150F Gearbox ratio of 2:1 (please check that is correct?)
wot range of 5-6 k.
get 5500 wot 5400/ 5500 at normal boat loading is where you are aiming for...So this prop is pretty much spot on... If slip numbers are correct
14 1/4 x 174800 = 33 mph 1.4km/l 11% slip ? 14.6%
based on a 2:1 gearbox ratio
4300 = 29 mph 16.2%
I do need the WoT rpms/ speed
Gearbox ratio of 2:1 (please check that is correct?)
With the engine at that height and assuming the height is correct or close I would be looking at 14 3/4 diameter and a prop with a little more cupping.
the cav plate sitting 35mm up fm keel bottom-
That is a flat edge placed along the keel under the boat and measured up from that line? and the engine trimed vertical..that is the transom is about 12.5 degs off the vertical. Thats the std lean of most transoms.
rule of thumb at 300mm 1 inch up suggested it was indeed I hole ( 20mm) Sort of kinda.
When the boat is on the plain, the ware from under the keel is lower than the normal sea level. As it comes out from under, that level rises in an elliptical curve.. therefore the 1"/300mm doesnt quite work..
Now throw another curly in the faster the boat goes the less distance the boat keel is below the normal sea level.
Not only that the elliptical curve distance behind the boat becomes greater..
You will also find that on the east coast, no bars, and bit different swell chop combo, different comfortable cruise speeds, also means a different engine height.
So you have now moved the engine up one notch, which changes the above numbers correct?
Old school 'tuning' rule of thumb, be it a hot rod what ever, always make one change at a time... a lot of experience one can maybe make 2 , even then depends on which 2.
Engine height , you only every do by its self.
So take it out, you will most properly find will pull another 4 to 5mph top speed, and associated rpms..equivalent of unloading maybe 200kg out of the boat
Run some wide turns each way see if any ventilation, the tighter and fast it will..bit of commonsense / judgement here if it is all good.
On flat water normal load..
Set rpms to approx 3200.. trim up till just before ventilation or porpoise.. note the rpms and speed
Do not try to get data right on the 3000 or whatever..
Then take up to around 3800, re trim up note rpms and speed
again 4500 5000 and wot.
Best way for crew or you to note is a felt pen on the dash.
With raising the engine you should also get a bit of a drop in your slip numbers, rpms move up a little, that means a little more power thru the rpm range, and with that a little more speed to rpms numbers.
Which has a very good likely hood that this current prop will be close or damn near bang on.
Just crunching some theoretical numbers after a engine lift and assumptions like boat gross weight 1700, WoT will be about 43 mph on that prop damn near puts it as the right prop...
So slow down get data then go from there.