does the 19.6 have a hook to cap top speed?

[1985aquasport196]

Hello,

  I recently installed a 2 stroke suzuki dt 225 to my 1985 19.6

Using prop 14.25x 19 w.o.t. = 48 m.ph. 5400 r.pm
using          14.25x22 w.ot. =48 mph      5100 r.pm
both acheive top speed with throttle not full engaged. once full engaged no further top end speed.
I m not trying to win any races lol and typically prefer to cruise at 32- 35 mph.  just trying to properly determine what is going on.  Any comments would be helpful.   factory shop manual calls for 14.25 x  16 thru  26 pitch. 
On a side note .  I recently rebuilt transom & raised height to 25" ARjay 6100 cool stuff.

Thank you.

[mshugg]

I think, if anything, these Aquasports had just a bit of rocker.  Hook would have the effect af pushing the bow down, and creating a tendency to bow steer - not good.  Are you trimming the motor up.  Some hook would not be unusual on a 34 year old hull, particularly if the trailer wasn’t set up to support the hull well. If you fix it, you may get a bit more speed.

If you’re hitting 48 at WOT, you must be at about 30 backed off to about 2/3 throttle.  That’s all these boats were designed for.

[1985aquasport196]

Hello.
48 top speed with motor trimmed.
You are correct.  about 2/3 of throttle and going wot raises rpm but not top end speed.
I do feel the bow does have plenty of rocker.


   Just surprised that no top end past 48 mph [gps]  with 2 different props . 14.25 x19   & 14.25x 22

Thank you

[McAllgeyver]

These hulls did not intentionally come from the factory with any hook capping the top speed. In fact, the story goes way back, and these hulls where designed in a way to create higher speeds.  But.... there are a lot of variables.  Trusting that you ran your boat in the same conditions, same wind direction, no current to speak of, same number of people/gear/gas/coolers, and obtained your speed from a GPS, I ran these numbers.
With your 19" prop you're at 91% efficiency(9% slip). If 100% efficiency, theoretical speed would be 52mph.
With your 22" prop you're at 84% efficiency. If 100% efficiency, theoretical speed would be 57mph.
There could be a few things that cause this like motor too low in water or props are for different applications. Maybe you unknowingly added more weight to the boat or put on a T-top on it during the 22" prop testing. That T-top creates a lot of drag and will absolutely reduce your efficiency.
Blue Agave, here on CA, would be your best bet to really see what these boats can do with high HP. I think he has his set dialed in.

[wingtime]

These hulls were not made for that kind of speed.  So anything above upper high 40's all bets are off.  They are most efficient at about 28-30 mph.  That is just the speed where your drag curves meet and is the sweet spot.  Going much faster takes more and more brute power.  225 is a bunch of motor for a 19'6 not only in HP but in weight.  200 is more than enough.  I've been On Blue Agave's boat a bunch of times, he had a 200hp two stroke and repowered it with a 150HP four stroke.  Amazingly his top speed wasnt that much slower (hole shots was less of course).  Of course his boat started life as a 19-6 but it's heavy with an enclosed transom, tower and flotation bracket... so his numbers will be very different.  He'll chime in though.

[boatnamesue]

Re: Prop Pitch
Need to know what your motor spec rpm range at WOT
Dial in pitch for prop that gets you to the top end of spec
Water test to be conducted w/avg load and calm conditions
Rule of thumb: For every inch pitch = 150-200 rpms (increase pitch to decrease rpm, vice versa)
Rule of thumb: Speed is not a reliable metric when troubleshooting engine/prop issues. Too many variables will effect speed....weather, load, air temp and humidity, etc.  Rpms provide you with a key hole look w/engine performance.   And just as important, listening to what your motor is saying, so to speak....sound emitted from a 2 stroke especially, these will give you fantastic insight of performance. 

Re: Throttle
Not normal to see no increase in rpms with throttle from 3/4 to full
Perhaps the throttle cam/lever/roller needs to be sync to spec

Also, is there a change in motor sound as you increase from 3/4 to full?  If no, then throttle system def needs adjustment.  If motor sounds like its working harder from 3/4 to full yet no increase in rpms, check compression. 

[1985aquasport196]

Thanks a bunch.   The suzuki dt225 2 stroke is beastly power for a 19.6 you are correct.  the weight of motor is reasonable however, 470 l.b same power head as 150 & 200] still lighter than 4 stroke 150 h,p,[or similar weight]
" I previously had 2 stroke 150 evinrude. 385 lbs

The transom height has been changed to 25"

Take care.
rob.

[1985aquasport196]

Good morning, 
rpm in shop manual calls for 5000 to 5600 rpm

propeller range in service manual range 14.25   pitch from 16 up to 28
 
the previous owner i purchased motor from had a 21 foot wellcraft,  much heavier boat than A.S. 19.6
He gave me his near brand new stilletto 14.25x 19 pitch prop.

I water tested motor on his boat we did 45 mph @5600 rpm 3 people.
With my A.S. same set up 48 mph rpm @ 5600

I purchased second prop 14.25x 22    rpm 5100 speed 48 mph.  speed same rpm properly dropped with increased pitch.[note with both props roughly 3/4 throttle top speed reached.  [motor trimmed]  more throttle engine rpm  increase but not in top end mph.]

The motors compression is near factory on all cylinders..

Thank you.
Cheers

[wingtime]

Your lugging that motor at 5100 rpm withe the 22". Your better off with that 19" pitch. The 22" will have have a slower hole shot too. The higher the up in the wot rpm range the better. I'd rather have it slightly over RPMS with a light load. Lower rpms will have a crappy fuel burn and will build up carbon.

[boatnamesue]

Sounds like your 19" @ 5600 has you dialed in.  As far as throttle, sync and time carbs then verify throttle roller reaches top of cam lever.