WTB propeller 19 pitch yam/merc

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    Posted: 07 Jun 2020 at 2:10pm
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Hi looking around for a 3blade 19 pitch prop 14 " dia to 14-1/2 in dia to suit a yamaha 150 f . I thinking someone in this forum thread could likely have an old one in their shed   Calcs tell me it suits what I'm looking to acheive but I wont actually know until I'm on the water hence looking for a reasonable priced 2nd hand one. -thanks in advance
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Post Options Post Options   Likes (0) Likes(0)   Quote F1SH3N Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jun 2020 at 3:58pm
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If you find one, i would like to test it also.
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Post Options Post Options   Likes (0) Likes(0)   Quote davv Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jun 2020 at 4:00pm
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Roger that, what area you live in ? And out of curiosity what type of waka /eng you looking g to try it on ?
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O think may have a 14 1/4 x 19  with universal center adapter (also most solaris and merc props now ).. just need to get the yammy washers for it.
 Will have to check later.
May also have a 14 1/2 X 19  and a 14 1/4X 21  if I find a 14 1/2 X 20.
Sort your diameter (grip) slip numbers before  sorting out your pitch.
There is significant difference between a 14" and 14 1/2"  .. definitely enough to make you think you may needed any thing from a 17 thru to a 21" pitch if dont actually get good data and crunch numbers.

 What is the current prop?
I get good data of it, and is in ball park ( WoT in or close to the Max rpm range) then with experience can calc the correct diameter and pitch together.

There are many older threads that give instructions on how to get good data to crunch.
 If not sure cant find or understand please ask and will sort for you.


 Going on the the request for a 14 to 14 1/2" X 19 on a 150 hp you would have around a 1200 kg total gross weight on the water (ppl gear everything) general use,  planing hull   cabin boat... which puts it around a 5.5 5.8mcabin ???
 A WoT speed at best trim for that boat around the 45 to 50 mph depending if engine is too low or not

 Very important thu.. the engine must be correct height before even thinking about propping. Most issues start here, and usually too low.
 Too low or to high by 1" (1 notch) can make the difference on a boat that size around 150 to 175 kg in equivalent gross weight on the water
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Post Options Post Options   Likes (0) Likes(0)   Quote davv Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jun 2020 at 9:12am
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Hi , Its a Senator RH620 with a 2015 yam 150F with a 14 1/4 x 17. Its just never felt quite right compared to other boats I've had hence a lot of research and talking with other senator owners similar set ups. the 150 has an OEM wot range of 5-6 k. I can get 5500 wot presently and est my set up to be 1300kg on the water. At best I can get 1.4 km /l where others seem to be able to get closer to 1.7/1.8. I get 1.4/l at best and it usually sits more around the 1.3/l. have checked the fuel out/in of tank and it seems to match with 50l for 70 kms ans motors running fine ie nothing like the choke half on etc  My use profile is light loading with no bars to cross
some figures
4800  = 33 mph 1.4km/l   11%  slip ?
4300  =  29 mph 
 
4000  = 26mph
Its been suggested that I raise the Ob one hole when another 620 owner saw where it was sitting( 1 up) . Upon measuring the driveshaft its about 550 on the pob back from the rear with the cav plate sitting 35mm up fm keel bottom- rule of thumb at 300mm 1 inch up suggested it was indeed I hole ( 20mm) to low so Ive moved it up one notch to try- all going well that could net another 150rpm at wot. I understand how if its too high now it will cavitate  etc
Ideally I would try a 14 x 19 as Im guessing to gain another 100 rpm fm the 1/4 inch reduction in dia but losing 3-400 going up 2 pitch sizes.  My calcs have this set up at somewhere at approx.  5350- 5400 (with the extra from raising the engine as well)but wont know until I try it as its all theoretical however I do know an owner with my exact set up who ran a 19p and loved it. Obviously if I retain the current prop dia of 14/ 1/4  I could be a little low in wot though. I'm no propulsion expert just been around boats for years and worked in tech/mech jobs all my life so can read and interpret figures reasonably well. I enjoyed reading your reply and would be interested in your thoughts. Ack I didn't catch the wot mph the camera blurred too much
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jun 2020 at 11:11am
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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 17
4800  = 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 boatWink
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.Wink

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.
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Post Options Post Options   Likes (0) Likes(0)   Quote davv Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jun 2020 at 3:43pm
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WOW - thanks so much for all your time , I couldn't figure out why the slip I had was 6% different ,- I had used a different gear ratio. upon checking the one I used was incorrect and it is indeed 2:1 which comes out at the 16% you've got
 
I'm hoping to get out this wknd so will collect all the figures and pass on.  It will be interesting how the rest of the figures and the increased height of the motor effect it all. Yes agree just trying one step at a time too.
 
thanks
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jun 2020 at 5:19pm
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WOW - thanks so much for all your time

 People current and past, even now pasted on, have been very good to me here and others...
And not just info..

And I dont have to get the old side rule out anymore, I tought myself how to and made a app I can just plug numbers in and get results ..even reverse engineer so can see what happens if...

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Post Options Post Options   Likes (0) Likes(0)   Quote davv Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jun 2020 at 8:37am
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Hi Steps, So the weather was kind enough to let me out on the wknd Smile
 
some figures I noted were
 
WOT  6000- 42mph ( almost felt like it would spin past 6 if the limiter didn't engage) I didn't like that at all..
3800- 24mph
4300- 29mph
4500- 30mph
5000- 35mph
at 3200 it seems to lose bit to cavitation at 17mph.  Turns were definingly less positive
 
I didn't manage to get pics but it definitely feels like its lost some bite when accelerating, and just generally felt lighter on the water somehow. I did notice in reverse when idling there was a pulsing harmonic which shuddered the whole boat. I've checked the tightness etc of the 4 mounting bolts and all is secure.  It disappeared when the rpm was lifted but its something that I've never noticed previously.  Additionally I was struggling to get 1.4/l at best with 2 POB.  Its such a big tank @190l its hard to know it the fuel meter is out without running a separate smaller tank. I did use a rod before and after as it will drop right down from the cap to the bottom of the tank and it would seem to indicate the flow meter is pretty close ( without being exact) using 30.1l for 42 km. Maybe this is normal and if so all is good , its just not what I'm hearing from some others ..   I've added up my hull ,motors, fuel, batteries accessories  etc and come up with 1600 kg with 2 POB
 
When the eng is trimmed right in the driveshaft is 520mm ( steering column 450 back)from the rear of the hull and the cav plate is 30mm above the bottom of the hull using a straight edge.
 
Id be interested in your thoughts, As  expected it felt very very different just not so sure it was in a good way . Fortunately though I have only changed the one thing so simple to reverse and or maybe diagnose  
 
 
 
 
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jun 2020 at 12:13pm
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Titanium
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Just moving info down here for ease.
 Check make sure is correct please.
 I like the mph.. saves me converting for calculations

yam 150F
 Gearbox ratio of 2:1
Prop  14 1/4 x 17
wot range of 5-6 k
get 5500 wot engine low
 Engine raised 1"
 Estimated gross weight on water 1600kg.


Calculated weight @ 6000 rpms 42 mph puts about 1700/1750kg.

WOT  6000- 42mph ( almost felt like it would spin past 6 if the limiter didn't engage) I didn't like that at all..

You see here just how much difference lifting the engine makes..And why this must be correct.

At normal cruise, at best trim, the cavation plate underside should be well in the water, and top side with a few droplets running down like condensation on a window.
3200 - 17 mph   34%  ok slip
3800- 24mph    21.5%  little to much
                                       19.2% 4000 = 26mph  too much
4300- 29mph   16.2 ok slip
                                         16.2%  4300  =  29 mph ok slip
4500- 30mph  17.2%  too much slip
                                        14.6 %   4800= 33  little to much
5000- 35mph    13 % little too much

6000  42 mph   13 % too much

at 3200 it seems to lose bit to cavitation at 17mph.  Turns were definitely less positive..

Slip numbers high
1/ The 4300 and 4500 data is suspect, as if around the wrong way ??
2/ The 5000 and 6000 data also suspect...
 a/ It could also be as if the trim was set at lower rpms , then go to the next increment and havnt re timed up???
b/ Or the engine is now too high ??

 Would have liked to see pics of the cavtiation plate at cruise at best rim for that speed.

When the eng is trimmed right in the driveshaft is 520mm ( steering column 450 back)from the rear of the hull and the cav plate is 30mm above the bottom of the hull using a straight edge.

level the boat with a level.. take the straight edge from the stern end of the keel to the bow about 0.5 m
 Now put the engine trimmed vertical (plum line, not right in)
A straight edge from under the keel to engine leg.
Dist from keel to back of the leg.
 And at that point  the vertical height to bottom of the cavitation plate..
 Dont get too carried away with this.. it is general rule of thumb to setup starting point then establish correct height..

 Was this engine height set at the Senator workshop/ agent.. if so they generally get it right.


definitely feels like its lost some bite when accelerating

It should , if good height, get up over the bow wave bit quicker, then pull away... if not could be too high, or not timed down. and ventaling slightly ???   if so you should be able to just hear it as a background sound..

Id be interested in your thoughts, As  expected it felt very very different just not so sure it was in a good way...
...

just generally felt lighter on the water somehow.

Yep like taking 1 or 200 kg out of the boat...
 It will feel very different....that is how important engine height is...

I did notice in reverse when idling there was a pulsing harmonic which shuddered the whole boat.

 engine trimed right down?

What was it like in sweeping slower cruise speed ( approx 3800 rpms) turns?  And trim down a smidgen as do so, any ventilation?

Im going to put this in, you may know..
 Trim..
 Trim is your most important tool.
 
When taking off, trim right down, boat goes over the bow wave.. dont touch throttle .. trim up to just before porpoise or ventilation.... you may have to adjust rpms to cruise speed, if increase, do so, then re trim up.. if decrease trim down
 You come to a wake , line up and trim down hard as go in, trim up on the other side...if not cruising at excessive speed
Everytime u increase or decrease speed, you have to re trim for THAT speed.
 Do a turn , need to trim down a smidgen
In chop, if boat is well powered, most of you work will be triming up and down.. the latter as the bigger wave comes in.
Even if the boat is set up right, if dont work that trim to best trim, this effects economy hugely..
 Correct trim also effects data for choosing the correct prop

Do not get too carried away with what joe blogs is getting..ppl have a tenacy to take the best of the best numbers rather than real numbers

 Do not get tied up in L/hr etc.. Its like a general use car that stops starts idles, accelerates, cruises...end of the day it is you old fashioned  miles per gal over each, and accumulated trips.
Spot L/h or for a trip is good if say a tractor going around and round a field turning hay, or ploughing constant load all day.
Also you can get very good mileage in a boat by  over propping (to high pitch.. ie the engine doesnt reach or only reaches min max rpm range under normal boat load.. thats ok till you put an extra person in or weight.. then the powerhead get overloaded right thru the rpm range.... Dont do it.

30.1l for 42 km.... that is pretty damn good mileage

IF the engine is now correct height.. (I strongly suspect its now high or triming not being done correct)
 And IF most of the  the data is correct.
If WoT is 42 mph.
You would need a 14 3/4 to 15" diam prop  (drop slip and WoT rpms back) with a 17 or 18"
 The bigger diameter at this height if high will cause even more ventilation.
 Another reason why I suspect the engine now too high or not trimmed well
It is normal when establishing engine height, to go one high.. you then KNOW and not THINK it maybe too low.

It is so important to get very accurate data...
 What info and data have is not quite adding up... to nearest 50 rpms.. nearest mph.. km/hr the convert is even more accurate.

 Sorry been writing this between doing other stuff.. so maybe a bit dis jointed...

Based on the above , even considering some of the data I have a gut feeling and this is very common, triming maybe not well understood?   or engine is now high
 Correct trimming is such a common issue even with long use boat skippers.
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Post Options Post Options   Likes (0) Likes(0)   Quote davv Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jun 2020 at 9:20am
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Morning Steps  -again thanks for your time , data diagnosis and thoughts it is appreciated and I have learnt much through this process.  I have a good understanding of trim and was trying to adjust as we went up/down the rpm/speed range to get the best data I could and 42 mph was the best I could get. The water wasn't dead calm which did make things difficult and may have contributed to some of the numbers being slightly less than expected.   It surprised me I got another 500rpm on WOT and not 2-300 rpm  I think a message may be in there there regards to eng height along with other observations. I'm probably going to leave it where it is for one more trip but gut feeling is I will end up dropping it back down a hole- nothing lost and a simple 1/2 hr task.  I'm glad I went through this process as I will know that it is optimized and put my time into thinking into other things. Will still try and get the photo of the cav plate when out next time. Your statement below may be the golden nugget out of all this
 
It is normal when establishing engine height, to go one high.. you then KNOW and not THINK it maybe too low.
 
 
 
 
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jun 2020 at 10:07am
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Titanium
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I have learnt much through this process.

 Thankyou I get criticized for my long winded explanations..and that is why I do it

The water wasn't dead calm which did make things difficult
 A little surface chop is ok, just got to be careful at high speed..and that where my  "felt tip pen and right on the bulk head, big letters" comes in.
 Look around for a bit of lea of land, behind a point or island.
My Favourite spots are is Waiheke channel and heading upto and past Clarks beach to Matakawa from Te torro ramp

It surprised me I got another 500rpm on WOT and not 2-300 rpm.
 I think you may have got a bit more than that...this is a classic illustration of why to set Max rpms at normal boat loading.. engine up 1" equivalent to 100 to 200kg (depending on boat size and commonsense)
So if have few more crew, and gear, dont drop below the min rpms. and if head out solo, dont go over.
Reputable workshop will set to max rpms on a basically unloaded boat and 1 or 2x 75 kg ppl

I'm probably going to leave it where it is for one more trip
 A big yes...'measure twice cut once'

was trying to adjust as we went up/down the rpm/speed range
 Dont go up down, just confuses matters at the helm.

Get just on the plane, start there.. trim up till just ventilates or porpoise, trim down slightly..note rpms and speed
Increase rpms about 4 or 500...adjust trim up again to just porpose or ventate, trim down slightly , take rpms and speed.
 Another 4 or 500 rpms and repeat to WoT

You will find once get to fast cruise speed, 4000 /4200 rpms, if the boat is ball park propped or better, you will have the 'feel' for the trim, and will only change a smidgen thru to WoT.
 Side note on that.. If played with Crouches formula, you will notice the hull constant doesnt hardly change from fast cruise up on a general use boat.
 OH and if play with crouches , you will find the 'published' original constants by crouche are way out.
 This confused me big time in the early days. Crouche made the formula around 1923...back then our 5 plus meter boats where moored, not 'trailer boats'.. Trailer boats have limited beam due to road rules...less friction area because of that plus the bow wave is further back towards the stern.Wink
So it follows the faster you go , less contact with water, less friction, the constant increases.
 Also on modern trailer  planing boats from early 60s on there is very little difference in the constant regardless of hull design.

 Just another snippet background info.

 Another: Newtons (apple fell on his head guy) Law of physics (think 1st one) says a given force (HP) applied to a given weight (including friction etc) will move that object at a constant speed.

So it would follow if at WoT you have 150hp @ rpm peak (5500 rpm) your boat will travel at X mph..regardless of the prop (if in ball ark thu.. bit commonsense here)
 It therefore follows if change it around.. if you know the speed and know the HP , you can calculate the weight of the boat.  Wink
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