Nineteen Speed Test

[bugdewde]

-1979 Aristo Craft Nineteen
-Mercruiser 470 4-cylinder 170 HP.
-1.84 ratio outdrive.
-23 pitch prop
-Loadout: 1/4 tank fuel, one battery, some inflatables, one 200 lb man and one 40 lb dog.
Almost a direct ratio on rpm vs speed. 2000 rpm is 17 mph, 2500 rpm is 23 mph, 3000 rpm is 31 mph, 3500 rpm is 34 mph and 4000 (WOT 4200 rpm) is 41-43 depending on trim and surface conditions.
Soon to post a comparison of the 25" Pitch prop I recently purchased.

 

[luva63]

Great run,Dwight! Really lovin' the color of your nineteen. Put the top back on mine the other day. Bet that will slow it down some. That sucka's heavy!

 

[bugdewde]

Here's the update with the 15 x 25 prop.
Same loadout except for a full tank of fuel.


3000 rpm was 35 mph
3500 rpm was 41
4000 rpm was 48

Surprising find........... with the top slid back, the top speed was only 46. Must act like a sail and catch wind.

 

[luva63]

I noticed the same thing with my top slid back on mine. Slowed mine down to about 44 mph. I just installed some smart tabs this afternoon. Might get to test them out tomorrow or next weekend.

 

[bugdewde]

Wide Open Throttle (WOT) cruise with the 15 x 25 prop at approximately 4,000 rpm.
This boat likes being trimmed in the fully out(up) position.
Max speed of 48 mph (only with front windshield closed... @ 1:30) with a full tank of fuel, some normal required gear and my 50lb Black Mouth Cur, Elwood.

 

[ziggy]

both yer boats are faster than mine.
couple things that may make mine slower. i think my engine is tired. while it's still servicable, mostly, compression on a couple cyls. is getting close to min. spec. think i got one at 115 and one at 120 psi. 100 is not servicable. my spread is a little wide too. my high one is 135-140. so, not the best. however. i still reach wot spec. for the 165 L6 that'd be between 3900-4300. i reach 4300 with a new 14.5'' x 19P aluminum black max prop.
the speeds have always been the same for my boat. while on plane which is about 2100rpm for my boat. my speed is equal to my tach. so. 2500 rpm and i'm doing 25. 3k rpm. i'm doing 30 mph. @ 4300 i'm doing 43 mph. these are gps and my factory tach. i've not been able to use a 21p prop as, predictably, it drops 400 rpm. so @ wot w/ a 21p prop on my boat. i can only achieve 3900 rpm. personally, i like to have my engine able to reach top end of wot spec w/o a normal load. begdwede, fwiw. yer engine spec is 3800-4200 (per s/m #3), so your perfect in your range it appears. + being able to turn a 15''x25p. that's great, i didn't know a 470 could do that. sweet.

to that end. i'm wondering bugdewde how you account for your non loss of rpm while going from a 23p to a 25p? i watched your videos. very nice and i can see your gps speeds and your tach. but from what i understand about props, when ya go up in pitch 1'' ya should loose 200 rpm. 2'' and ya loose 400 rpm. when i went from a 21p to a 19p. as said, the 21 produced 3900rpm, the 19 produced 4300 rpm. to me this was predictable. yours didn't do that. do ya have any idea why?

both ya guys got great boats and i love your colors. glad to have ya around to help others when they have questions.

 

[luva63]

44 mph,46mph, 48mph. When you get to that speed,all those numbers are just that... numbers on a GPS. I think my boat is going pretty fast and then a bass boat with a 200hp outboard blows by me at 75mph

. Kinda put it all in perspective.LOL. Ziggy,as nice and as great condition your Nineteen is in And your getting 44mph out of it . I'll trade my 46mph for your beautiful trim ANY DAY

Jim

 

[ziggy]

44 mph,46mph, 48mph. When you get to that speed,all those numbers are just that... numbers on a GPS. I think my boat is going pretty fast and then a bass boat with a 200hp outboard blows by me at 75mph

. Kinda put it all in perspective.LOL

agreed, but you guys do have some fast boats. by todays standards, my 43 mph is pretty hohum. everyone goes faster than me... that's ok though. i'm gettin older and speed matters less than it once did to me. i use lime time as a pleasure boat anyways. generally not going to darn fast. or, i could say i have more fun out in the nasty weather than i do racing from one end of the lake to the other. i did my speed fix on jetskis in the past. i just want my boat to run proper and get me though them nasty days. i get more satisfaction with that these days.

 

[luva63]

I know when I was pushing on my nineteen at WOT, there was another thing that was moving pretty fast and that was the fuel gauge needle towards empty . I found it's alot better to cruise around 25 -35 mph. At least you get to ride longer. I kinda like giving the wheel over to my wife so I can sit back and enjoy . jim

 

[bugdewde]

I think my non-loss of rpm is due to the fact that I don't think I took the 23 prop all the way "out" in trim..... like I did with the 25. I bet that if I trimmed the 23 all the way out, it would over rev. I seem to remember it porpoised when I trimmed it up with the 23. I may have to retest it. From what I've gathered about the 470, it's a real torquey engine. These overly huge pistons (basically, 1/2 of a Ford big block 460) crank out some power. Aristo Craft says it was their most powerful and fastest engine available in a Nineteen. Some internet reading revealed some 470 flaws and benefits. Most engineers have learned not to exceed 2.5 liters for an in-line 4 today. Well, the Mercruiser guys just didn't "learn" that very well by chunking a monsterous 3.7 liter engine in there. I suppose that torque allows it to turn the large 15 x 25 prop without issues.