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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2018 at 7:53am
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Titanium
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WOT 5400-5500 is roughly 63-65km an hour (40 mph)
 I would expect if propped well AND engine correct height would get 42/ 44 mph for normal 3 ppl plus gear loaded up.

 Subject to accurate data, and at best trim on flat water, normal load
That is well powered...It looks as if the prop diameter / grip is a little low...and/ or the engine mounted too low
If grip/ slip and engine height was correct you Will have 15" or 16" pitch prop...
I would guesstimate the correct prop for that engine combo would be more in the 17 to 19" pitch ball park with engine at correct height.

Then looking at 
4000-4500 is around 45-47km an hour (29mph).. assuming accurate data at best trim on flat water..
 This again if prop grip and engine height right would be about a 15" prop at correct grip.
 With a 17"/ 19" prop and engine correct height, that would be around 33/35 mph

 Also of huge significance to fuel economy.. cruising at over 4000 rpms, even with good engine height and propping you will go thru a huge amount of fuel... as to travelling 1n the 3800. 3900 rpm range.
 For example If I travel at 4000 rpms (very well powered) and cruise 37/38 mph over any significant (1/3) distance within approx 35nm trip, as to traveling at 33/35 mph at lower rpms will increase my fuel Liters bu 25 to 30% straight off.
 Good engine height and propping normal load at best trim cruising 3900/4000 rpms on flat water subject to more accurate data you would cruise around the 30/ 31 mph around on ave 1nm/ L 

 Stuff /data required.
1/ Accurate speed/ rpms  each at best trim for that speed on flat water in 1000 rpm increments (preferby 500) from around 3000 rpms to WoT at normal boat load.
2/ At normal cruise ..approx 4000 rpms,.. normal load , best trim wave the smart phone camera around the engine leg showing the water around the cavitation plate.
3/ The current prop specs..pitch and diameter



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Post Options Post Options   Likes (0) Likes(0)   Quote tiras Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2018 at 6:39pm
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Current prop is 17in pitch. Will definitely look at engine height as I suspect this may be the issue.
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Post Options Post Options   Likes (0) Likes(0)   Quote clawman Quote  Post ReplyReply Direct Link To This Post Posted: 30 Dec 2018 at 7:49pm
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waiting for the wind to die down here in wgton so heres some figures for my 5.45m aqualine with a yammy 100hp  4 stroke on the back.
recent trip home from mana on dead flat sea + prop trimmed out. 2 of us on board plus snorkel gear so boat not heavily loaded.
4800rpm gave 42km per hour + flat out got up to just on 6200rpm for 61km per hour.
prop is a 13.5 inch  x 15 - k + motor is on top notch
i have done 250 hours since new + fuel consumption is roughly 2km per litre.
it has a 45 litre tank so i reckon if i ran it dry i might get up to 100km for a trip.
best speed seems to be about 40-42km per hour + rpm about 4800 - 5000rpm depending on load + sea.
40km per hour is plenty fast enough to get where you want + not chew the gas.
do these figures sound about right- boat gets up on the plane no problem even with 4 divers on board
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 30 Dec 2018 at 10:46pm
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Titanium
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yammy 100hp  4 stroke  2.31:1 gear ratio  correct?
 Max rpm range 5000 to 6000 rpms .. Correct?
prop is a 13.5 inch  x 15

4800rpm gave 42km/hour   26 mph

If those numbers are correct you have a slip of 0.7% which means you are going faster than the prop is turning
you should for a general purpose  boat that size have a slip at cruise around 12 to 15%
 If the diameter is corect to grip and 15" pitch you would be traveling approx 22 mph.. 35 km/h

WoT  6200rpm for 61km/hour. 38mph

 That gives a total weight approx 1100 to 1200 kg which is in the ball park for total gross weight for that boat.
It gives a slip of 0.3%...which is also very unlikely...if propped well 4 to 6% 
 If assuming height /data correct then on the over reving to 6200 WoT a 17 or 18 pitch prop would be more suitable ,
And would also apply to WoT 

 boat has the wrong prop.. assuming engine height is correct.. most likely pitch and diameter.

 There is something wrong with the supplied details/data

fuel consumption is roughly 2km per litre.
Thats ok moving that weight on the plain at that speed.


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Post Options Post Options   Likes (0) Likes(0)   Quote clawman Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2018 at 8:52am
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hi steps
cheers for the feedback- do you think it would be worthwhile trying a 13.5 inch  x 17 prop + see what the difference is.
i assume that with the right prop i should only get 6000 rpm at wot + top speed would be more.
same would apply at cruising speed of 4800 rpm + fuel consumption would improve also.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2018 at 11:50am
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Top speed will be the same regardless of the final gear ratio.. (pitch) the gear ratio determines the time you get to that speed.
 top speed .. basic high school physics is a give hp will move a given weight at a given speed 
 Hence how I can calculate your gross weight on the water.

You should be aiming for midway in the manufactures rpm range , or marginally below that point for a general use boat at normal load..
This then gives the correct loading on the power head right thru the rpm range... If happen to load up heavy.. you are still in range.. if abnormally light.. still in that range.

Without full normal accurate data...and knowing  engine at correct height.
ie rpm and speed from approx 3000 rpms to WoT in approx 500 rpm increments.. at best trim for each speed/rpms on flat water , boat normal load.
 As speed increases you are able to also trim up.

1st thing that should be correct or ball park is slip at WoT.. it will automatically be right thru the rest of the range..
 
 "In saying that the chances are a 17" prop would drop the WoT rpms, and very likely also increase the slip...with fingers crossed same diameter or maybe 1/4" smaller...it maybe damn near back on

IF the data above is accurate and engine height right.
So yes it maybe worth picking up a 17" for $50 off trademe.
 Then getting good data on that.
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Post Options Post Options   Likes (0) Likes(0)   Quote clawman Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2018 at 5:03pm
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just to clarify what you are saying 
wot revs is 5500- 6000 for this motor so correctly propped at 3000 rpm i should be getting my normal cruising speed of 40km per hour?
appreciate the feed back steps
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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2018 at 7:58pm
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i just did the same calcs as Steps i think.

your noted top speed has you at prop slip of ~1%. its not a particularly fast top speed for that rig. i also note that you are over the manufacturers recommended max engine speed of 6000rpm.

did a dealer set up the rig this way - if they did - yamaha nz could with hold a warrantee claim because of over-reving engine.

if you could find a prop with another inch of pitch at 16" you would likely keep your 60kmph top speed but see revs drop 200-300rpm

your current fuel use isnt too different to what a yamaha 90hp 2stroke could offer - because your engine speeds are so high

with a 16" prop 4000rpm cruise would move close to 40kmph. obviously the reduced engine speed would allow better range from your small fuel tank
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jan 2019 at 1:03am
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Basically the same asd BH above
If your WoT is 38 mph and you are targeting say 5700 rpms as WoT then you should require a 17 " pitch prop  with a diameter (grip or lack of) WoT slip 5% 
about 23/24 mph (39km/h) @ 4000 rpms

I recon thu Wink
16" with drop you to about 6000 rpms 
about 22/23 mph (36 kmph) @4000 rpm

both are based on the only known data
hp  gear ratio are fixed, 
you have a near 0% slip which is not realy possible.
Slip/ rpms/ speed/ pitch calculations depend on each of these being accurate.. either speed or rpms is not accurate, or both

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Post Options Post Options   Likes (0) Likes(0)   Quote clawman Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jan 2019 at 9:48am
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thanks for the advice guys- yes the dealer did set it up but from memory he just copied what was on a previous sale he had done.
new years resolution is to find another prop as suggested + see what difference it makes
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jan 2019 at 10:25am
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yes the dealer did set it up but from memory he just copied what was on a previous sale he had done.

 So did not ask weight of ppl , what use going to be.. fish/ towing/ diving etc...
 Dealer generaly set up so under normal ave conditions/ weights.. say 3 ppl std ave weight 75kg, fuel, the very basic gear..to near max rpms
 The theory being the boat will be lighter than normal, and when loaded up the rpms, in theory will drop a few 100 rpms.
 Also when sea trialing / demo, and owners 1st trip, generally boat is light.. performs well which means lower cost of sale as smaller engine than intended end use..
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Post Options Post Options   Likes (0) Likes(0)   Quote clawman Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jan 2019 at 10:17pm
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took the advice of steps + others + got a 13.5 inch  x 16 prop for the aqualine
now do 4000 rpm for 40 km per hour instead of 4800rpm.
couldnt test wot as too rough at mana tonight.
also the motor does sound a lot better too.
shame i didnt do this 250 hours ago or the dealer a bit more proactive
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jan 2019 at 9:30am
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Asuming data is accruate on flat water at best trim for that speed, you are over propped as have a 5% slip at 4000 rpm @ 25mph (40km) cruise.
 5% is more the WoT slip.. you need to target 12 to 15% for that sized boat.
I think you may be pushing to reach the min manufactures WoT 5000  to 6000 rpms ..due to the low slip at cruise.

A reduction in diameter.. increase slip  to 12 to 15% will give a 4000 rpm speed around 24 mph (37 km/h).. and increase the WoT rpms...target for your  general use boat 5400/5500. @ approx 32 mph (52km/h) 

As some of the previous data is suspect.. numbers dont work.. impossble to happen.. and cause some considerable conflict in current calculations.

 To work stuff out needs accruate data.
 I repeat

"Without full normal accurate data...and knowing  engine at correct height.
ie rpm and speed from approx 3000 rpms to WoT in approx 500 rpm increments.. at best trim for each speed/rpms on flat water , boat normal load.
 As speed increases you are able to also trim up.
1st thing that should be correct or ball park is slip at WoT.. it will automatically be right thru the rest of the range.."


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Post Options Post Options   Likes (1) Likes(1)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jan 2019 at 1:32pm
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Originally posted by clawman clawman wrote:

took the advice of steps + others + got a 13.5 inch  x 16 prop for the aqualine
now do 4000 rpm for 40 km per hour instead of 4800rpm.
couldnt test wot as too rough at mana tonight.
also the motor does sound a lot better too.
shame i didnt do this 250 hours ago or the dealer a bit more proactive

good result - cost much for the prop?

i think 40kmh/23kts is a great cruising speed for a boat of that size.

should be a lot easier on the ears now...
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Post Options Post Options   Likes (0) Likes(0)   Quote clawman Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jan 2019 at 7:11pm
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prop cost $240 new so i just have to try wot when next out on a flat sea + see what the result is.
from the last trip it certainly feels like a lot more power available + you were spot on with your thoughts of 4000rpm for 40km per hour
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Post Options Post Options   Likes (0) Likes(0)   Quote Grasshoppa Quote  Post ReplyReply Direct Link To This Post Posted: 13 Jan 2019 at 10:45pm
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Out of interest Clawman, is the prop stainless steel or alloy?  $240 seems very cheap
You'll always get better performance out of stainless, better holeshot and prop will allow better trim without cavitation and porpoising due to blades not flexing as much
You seem to have satisfactory performance regardless however
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2019 at 10:08am
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You'll always get better performance out of stainless, better holeshot and prop will allow better trim without cavitation and porpoising due to blades not flexing as much

SS props come into there own with very high powered or bigger heavier boats....when moving at higher speeds.
There is little if any difference between a alloy and stainless on boats upto around 1300 kg at cruise speeds... as there is not emough loading on the blades to cause distortion.
 For general use boats, the extra load on the blades at hole shot is so quick and  over the bow wave to have any significant noticeable difference....The add into the exhaust thru the prop , designed to cause  slight ventation on hole shot, in the same manner as a hi stall torque converter to get a drag car motor upto higher rpms and power band, then grip.
 As to porpoising, it is rake that influences that, not blade twist... the fact that to sorce a high rake, usually 4 blade prop, the only source happens to be SS doesn't mean SS is better for  preventing porpoising

If one takes a general use boat around 1200/1300kg  and 115, 140 and 150 hps compare 2 identical props, alloy and SS, collect accurate data.
There is very little difference up to around a 35mph cruise, slightly more but still not noticeable or  significant in data, hole shot to 35 mph... Getting upto 37 mph fast cruise and to WoT, with the extra load on the blades then one sees an increase in change, MAY feel notiable if  look at your odometer and rpm gauges as the pitch decreases.. and a slight increase in fuel consumption.

 lighter boats where far less loading, and smaller diameter props used, nothing noticeable.

Getting up around 1500/ 1800 plus 5.8/ 6m boats that have larger diameter props (14 1/2") and blades loaded up it is then cruise speeds, performance and economy etc becomes significantly noticeable.

Selling SS props is rather profitable , espec when not really applicable..
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Post Options Post Options   Likes (0) Likes(0)   Quote Grasshoppa Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2019 at 10:57am
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Originally posted by Steps Steps wrote:

You'll always get better performance out of stainless, better holeshot and prop will allow better trim without cavitation and porpoising due to blades not flexing as much

SS props come into there own with very high powered or bigger heavier boats....when moving at higher speeds.
There is little if any difference between a alloy and stainless on boats upto around 1300 kg at cruise speeds... as there is not emough loading on the blades to cause distortion.
 For general use boats, the extra load on the blades at hole shot is so quick and  over the bow wave to have any significant noticeable difference....The add into the exhaust thru the prop , designed to cause  slight ventation on hole shot, in the same manner as a hi stall torque converter to get a drag car motor upto higher rpms and power band, then grip.
 As to porpoising, it is rake that influences that, not blade twist... the fact that to sorce a high rake, usually 4 blade prop, the only source happens to be SS doesn't mean SS is better for  preventing porpoising

If one takes a general use boat around 1200/1300kg  and 115, 140 and 150 hps compare 2 identical props, alloy and SS, collect accurate data.
There is very little difference up to around a 35mph cruise, slightly more but still not noticeable or  significant in data, hole shot to 35 mph... Getting upto 37 mph fast cruise and to WoT, with the extra load on the blades then one sees an increase in change, MAY feel notiable if  look at your odometer and rpm gauges as the pitch decreases.. and a slight increase in fuel consumption.

 lighter boats where far less loading, and smaller diameter props used, nothing noticeable.

Getting up around 1500/ 1800 plus 5.8/ 6m boats that have larger diameter props (14 1/2") and blades loaded up it is then cruise speeds, performance and economy etc becomes significantly noticeable.

Selling SS props is rather profitable , espec when not really applicable..

Wrong, 
This is where your theoretical calculations at a desk end and those who actually fully know what they're doing with practical experience differ
Performance between stainless and alloy may vary from application to application but it does differ, anyone who's know's how to drive and trim correctly will tell, thats why manufacturers actually offer and sell these options

Clawmans rig sounds like its performing satisfactory regardless of what prop its wearing but i was curious as $240 is pretty good buying, from memory the stainless is around the $1000 mark which i think is pretty excessive,
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2019 at 11:14am
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This is where your theoretical calculations at a desk end and those who actually fully know what they're doing with practical experience differ

 And that is where you are wrong..
1/ they are NOT my theoretical calculations
2/ Its not.. just theory its also several yrs now of practical application.. as you may see from real life personal examples I give..
3/ Then throw in navel architect such as Gerr keith Crouch etc.. who are established in the industry ....
And at least I give the reasons behind my statements..

Now you tell me how and why they statements and the top international experts of the last 100yrs are wrong...and why..

 
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2019 at 11:51am
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Clawmans rig sounds like its performing satisfactory regardless of what prop its wearing

Really.. the low slip numbers at cruise not an issue? If ther data supplied is correct?
Powerhead not being loaded beyond manufacturer specs... chances are will nt reach manufacturers  WoT spec, or at least very low into it?

 And you say "sounds like its performing satisfactory" ?
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