porpoising problems

[MWBROWN]

16ft Bayliner Fish and Ski (1984 model)<br />85 hp Force<br />13 x 20 pitch prop<br />speed wing on engine<br />5200 rpm @ 38 mph GPS<br />2 200 lb guys<br />gear<br />20 gal gas<br /><br />At top end, I can trim the motor up some to get more speed. A little bit more and it starts to porpoise. A little more and it gets real bad.<br />I raised the engine up 1 1/4 inch and the problem was the same but the prop would blow out while trimming, still porpoising.<br />I took the speed wing/whale tale off and the porpoising was terrible. There is no more holes to move up, and the original position was as low as it could go. The AV plate in the lower position was maybe an inch above the bottom of the boat.<br />I have read a lot of the discussions and do not see any answer to my problem.<br />Is it prop, or what? The only thing that is not original is the prop was 19 pitch, and it porpoised then also.<br />Need expert advice.<br />Thanks,<br /><br />Mike

 

[roscoe]

Re: porpoising problems

Originally posted by pewterwyz:<br /> A little bit more and it starts to porpoise. A little more and it gets real bad. ..... Is it prop, or what?

Just as it will if you trim any motor out too far.<br />So don't trim it out that far.<br /><br />You are running near the top end of rpm range.<br /><br />What are you trying to achieve?

 

[Texasmark]

Re: porpoising problems

I agree. If you want to stop porposing at a given trim setting you need more power to push you through it. So if you don't have anymore, reduce the trim setting till it stops.<br /><br />Now if you want to go faster you need a different hull type which reduces the drag and then would allow you to run a higher pitched prop at your 5200 rpm's and hence go faster. A good pad does just that, as do lifting strakes.<br /><br />Mark

 

[MWBROWN]

Re: porpoising problems

Thanks for the responses. In other words, I am getting all I can out of the boat and motor. I guess that is what I wanted to know.<br />I wanted a bit more speed if I could.<br />Being rather new to boating, I did not know if the porpoising was a normal thing while trimmimg or not.<br />I guess I will stop worring about it and just enjoy the boat. A question, would smart tabs help with more speed on this type boat?<br /><br />Thanks again.<br /><br />Mike

 

[stevens]

Re: porpoising problems

Adding Smart Tabs will stabilize the boat some at higher speeds, allowing you to trim the engine out some more than you otherwise could have. This may add a few MPH of top end speed, and very probably also a more stabile ride.<br /><br />You've got to lose the "speed wing" if you put tabs on her.<br /><br />Once you've added the tabs, these will help on your hole shot and you may then be able to move up a bit in propeller pitch. This might then also add a bit of top end speed.<br /><br />A lot of people here will testify to these effects - do a search...

 

[roscoe]

Re: porpoising problems

It all boils down to how much time and money do you want to spend, to get 1-3 extra mph.<br />$300, $500, ?? <br />And if you can go 3 mph faster, so what.<br /><br />I think you have the right prop for your boat.<br />I think you would be better off spending the extra money on maintenance and fuel.<br /><br />Happy boating. Enjoy.

 

[Tail_Gunner]

Re: porpoising problems

I am having some very similar problems, for my self i'm sure the problem is two fold. One solution is trim tabs, getting the stern off its *** and then a prop that will provide a lot of lift. Try searching lift on props both bow and stern or combined.

 

[MWBROWN]

Re: porpoising problems

Well, for one, I like to go fast, but money bucket does have a bottom. I had a thought that this boat might do 50mph with out a lot of money.<br /><br />I think I will get the Smart tabs for Christmas, and for now enjoy the boat as suggested.<br /><br />Thanks Roscoe, Tail_gunner, Texasmark, Stevens.

 

[QC]

Re: porpoising problems

I like your plan. As Stevens has suggested, add the tabs, lose the wing <br /><br />50 MPH will not happen unless you repower and gain at least 50 bhp . . .

 

[stevens]

Re: porpoising problems

Notice my careful use of words like "may", "a few MPH", and "a bit of..". In other words, be very realistic in your expectations of speed gains - it may not be much at all.<br /><br />But, then again, playing around with different props and tabs and set-up can be a lot of fun in itself.

 

[LubeDude]

Re: porpoising problems

Originally posted by pewterwyz:<br />I had a thought that this boat might do 50mph with out a lot of money.<br /><br />

You will need a good running 115 to get there!

 

[MWBROWN]

Re: porpoising problems

Boat is rated for max 90 hp. SO 50 is out of the question. Thanks for all the replys.<br />The original prop was 13 x 19 and I had it chaged to 13 x 20. It is real thin material. What does the flexing do to top end? I bought a used 13 1/8 x 15 that I could have pitched to 17 and maybe have it cupped. It is a Michigan Match and it is a lot thicker. Thoughts?<br /><br />Thanks again.

 

[QC]

Re: porpoising problems

Flexing slows you down at top speed, but can actually improve hole shot. Thinner blades and less flex are a couple of the big benefits of Stainless . . .

 

[stevens]

Re: porpoising problems

But you'd be better off buying a good prop rather than spend money on tweaking one that wasn't very good to begin with.<br /><br />Thicker blades will generally be slower and no amount of tweaking will change that.<br /><br />I believe you are at about 22% slip right now. Even if you got yourself some super prop that only gave you half that slip, you would only gain 3-5 MPH of top speed.<br /><br />Again, be realistic in your expectations of how much speed gain you'll get out of tweaking your setup. Often, the most gains can come from putting the boat on a diet..

 

[Texasmark]

Re: porpoising problems

Hey Stevens, "putting the boat on a diet".....<br /><br />I decided to do just that this time around. Last boat I had, I was ready for WWIII. This time I only take what I need for that trip.<br /><br />Totally agree with your thinking. Now I understand that if you are venturing out into harm's way, you should prepare yourself. But I'm not so I won't.<br /><br />Mark

 

[Texasmark]

Re: porpoising problems

Hey roscoe, <br /><br />"It all boils down to how much time and money do you want to spend, to get 1-3 extra mph.<br />$300, $500, ?? <br />And if you can go 3 mph faster, so what."<br /><br />That's what I asked myself before I spent another $250 for another prop after I had just spent $300+ for one. I wanted to break the 50mph hurdle and since my engine was running 6250 and rated for 5500 I had the power to spare to get there. Now that I did it, the challenge is gone. I still run WOT but not as much as before.<br /><br />Now if I (wife and I) was still raising 4 kiddo's I would have been happy to just have a boat. Grin<br /><br />Mark

 

[Ron G]

Re: porpoising problems

1 to 3 mph can be pure joy beating your buddies down the lake to that honeyhole,or just passing them on buy Seems i may have a speed problem

 

[MWBROWN]

Re: porpoising problems

It is nice to know that others thing that 1-3 MPH is a thing to go after. My friends boat will do 42-44 and I am tired of chasing him. I think the Smart tabs may do the trick. Now to talk the better half into it. LOL<br /><br />Thanks for all the tips. Sure is appreciated.<br /><br />Mike

 

[Texasmark]

Re: porpoising problems

Hey Ron and Pewter, we are on the same sheet......go after them. Grin.<br /><br />Mark

 

[Gary H NC]

Re: porpoising problems

You can get the (blems) from Nauticus Smart tabs..Mine had only one small scratch on them..130 bucks for smart tabs is a cheaper way to go than buying different props..When installed and adjusted you can gain 3 or 4 mph..