19'6 with a 115 yamaha 2-stroke - how fast should she go?

[Capt. Bob]

Start here.

http://www.classicaquasport.com/gallery ... 554/page/1

[fishgutts]

That is awesome!

On the "features" page, it says that this boat has "all fiberglass stringers".  If this is the case, then I would not have to worry about my stringers being water logged.

Anyone know if the stringers are "all fiberglass"?

[Capt. Bob]

That is awesome!

On the "features" page, it says that this boat has "all fiberglass stringers".  If this is the case, then I would not have to worry about my stringers being water logged.

Anyone know if the stringers are "all fiberglass"?

Your stringer system is fiberglass. They are hollow in the middle and filled with a low density foam for support and flotation. Water has a way of finding even the smallest of compromises (think screw holes) and soaking this type of foam.

[MarshMarlowe196]

Well, I just put on an old aluminum "spare" prop that came with the boat. Took the boat for a spin.... results have me more confused than ever.

RPMs were up where they should be: around 5700-5800.

Speed was still at 30 mph on the GPS.

What was the pitch on the "spare" prop?  If it was less than 15, then your performance makes sense.

A thought about waterlogged stringers-  Unless you have your boat moored, and your stringers had in fact soaked up enough water to be cause your boat to underperform (which would have to be a lot), why wouldn't the majority of that water run back out?  If it can find its way in, it should be able to find its way out, at least some of it anyway.  If/When you put your boat on the trailer, remove the drain plug- do you have a steady drip or flow of water dumping out??

[fishgutts]

I have no idea what size that prop is...there are no numbers on it.  
As far as the stringers go...have had the boat in the water for 3 days...when I took it out, there was no water in the hull... I still doubt this boat is water logged.  But, I would like to weigh it.  
I think my next step has to be a ss 17" prop.  I just need to find one to try out.

[fitz73222]

Hey Fishgutts,

Not to be alarmist about water logged stringers, but our boats made in the 60`s and 70`s all had this open cell type foam that collected water in the stringers as the years go by. It reminds me of the green foam that you use to make Christmas arrangements with, only an orange color. The main pathway was through the console hold down screws and seatback assembly. Now it seems that most rebuild threads you encounter they find wet foam in various stages of decay and absorbsion but always wet. The weight of the wet foam is always an estimate and it may mean nothing more than 50-100-200 lbs. Can the stringers hold 20 gallons of water each? Who knows? I didnt mean to light the fuse on the water logged concern; it was just worth mentioning. I would be looking at timing, throttle butterflies fully opening, has anyone been in the carbs recently? Plugged main jets from crap fuel? Do you know that your Stilleto hasnt been repitched if you didnt by the prop new? Stuff like that. I would be curious to see what she weights. Look at the brightside most Boston Whalers of similar vintage had the entire hull filled with this foam. Just think how nice a 4000# Montauk 17 must ride!

[gran398]

I don't know how much my 22-2 weighs, but she's heavy. Really heavy. And I'm confident the stringers are fully saturated.

She's scheduled for rebuild Nov. 1. For board input, I'll weigh her on the trailer before the work begins. Subtract the trailer and engine and gas weight. Then we'll have a pretty good idea as to the weight the saturation adds versus the 1975 published dry hull weight.

[fishgutts]

I checked the butterflies and looked at the carbs... Everything looks great.  The motor runs and sounds great.  I don't think the problem is the motor.  

The prop is now my main focus.  I am not sure if that stilleto prop had ever been re-pitched.  I will try to contact the previous owner and see if he knows.   I am just going to start asking around and seeing if some people have some different size props for me to try out.  Maybe I will get lucky and find one that works better.

Will keep trying!

[gran398]

Well, I just put on an old aluminum "spare" prop that came with the boat. Took the boat for a spin.... results have me more confused than ever.

RPMs were up where they should be: around 5700-5800.

Speed was still at 30 mph on the GPS.

What was the pitch on the "spare" prop?  If it was less than 15, then your performance makes sense.

A thought about waterlogged stringers-  Unless you have your boat moored, and your stringers had in fact soaked up enough water to be cause your boat to underperform (which would have to be a lot), why wouldn't the majority of that water run back out?  If it can find its way in, it should be able to find its way out, at least some of it anyway.  If/When you put your boat on the trailer, remove the drain plug- do you have a steady drip or flow of water dumping out??

Makes sense, if the water in the stringers was able to drain to the bilge. Unfortunately it cannot, as its encapsulated within the stringers. The water entered from above, but cannot escape from below. Think of it as a soggy sandwich, trapped within a freezer bag. Its stuck.

[fishgutts]

So, it looks like I need to buy a new prop.  I need some suggestions.

Is there anyone out there running this same boat/prop combo?

19'6  Aquasport (1972) with a 115 2-stroke yamaha.

I want to make sure I get the correct prop this time.  

Thanks guys

[akbridge]

There are pitch numbers cast into the prop.  They are cast into the hub.  It should say something like 31317 behind the nut that holds the prop onto the shaft.  I have one somewhere so I can show you....  
 
The numbers are cast into the inner most ring.  Sorry the picture was with my phone.
It may be that the motor is set too low in the water.  With that prop you should have the ventilation plate about an inch or more above the keel of the boat.  Also do you trim your boat out enough while running?  If you keep the motor tucked all the way down, she will never reach full potential.  Try trimming it up until she starts to porpoise or blow out then trim it back down just a little.

[fishgutts]

The motor is mounted at the right height and has a jack plate.  I do trim the motor up when I am running.  

The pitch of this prop is 15.  I also think my prop may have some additional cupping.  I am trying to find out what other guys with the same motor are running on their 19'6 aquasports.  Then, when I buy/try a new prop, I know what kind of numbers they are able to put up with that same prop and motor.  

Thanks for the advice though... these are good recommendations... just already tried them.

[akbridge]

This guy claims 26 knots with twin 70s.
viewtopic.php?f=6&t=5575

You may not be far off with your speed on an old 196 powered by a 115.  I run a 1971 170 with a 90 johnson on a jackplate.  I can generally get 39 mph.  You have a larger heavier boat with similar power.  I would try some different props and see what brings your RPMs up to an acceptable level.  Good luck.

[Aswaff400]

i ran a 112 hp johnson on my boat with over 1300 hours on it and averaged 37-38 mph with 2 people on board and 2 9 gal cas cans... i ran a 12.5x17 3 blade stainless prop and spun 5700 rpm easily...

[fishgutts]

Well boys... the problem is solved.

Please take it easy on me after reading this...

My GPS was set to Knots/Hour... not Miles/Hour.

I must say... I am very embarrassed to discover that my big problem was no problem at all.  But, I am also very relieved.

Once I changed the GPS settings, I am consistently getting 35-37 mph WOT.  

Thanks for all the help and advice.  Glad to know that I don't have soaked stringers and my motor seems to be pushing the boat just fine.