"Dolfin motion"

[Jet Blitz]

Hi Guys, I am pushing a 16,6 ft Deep vee with two 60 Hp Mariners. It runs well at 3/4 speed. When I open it to full throttle the boat starts a dolfin motion (Lifting the nose up and down). If I trim the motors IN, I struggle to plane the boat. <br /><br />The boat was heavy with fishing equipment (Nose). Do you think it might be under powered?

 

[rickdb1boat]

Re: "Dolfin motion"

Jetblitz <br /><br />A 16 1/2 foot boat should not have ANY problem with twin power. Sounds like your set-up is wrong or weight distribution is off. Where are the cavitation plates in relation to the bottom of the hull? So you are already on plane at 3/4 throttle and when you go to full throttle, it wants to bounce? Is this correct? And if you try to correct it by trimming in, it wants to come off plane. You may be actually overpowered. What is your speed at 3/4 throttle and what brand of boat is it?<br /><br />

 

[Jet Blitz]

Re: "Dolfin motion"

Hi RB, <br /><br />The boat is a Coast Craft, similar to the Ace Craft. Yes it starts to bounce when I open to full throttle. I do not have a speedo, by the boat is running fine at 5000 rpm. When I open up it goes up to plus 6500 and the bouncing starts. I starts of slowly and continues to get worse. It forces me to throttle back to 5000 rpm. It gets to a point where it it wants to jump out of the water. My trim setting is in the second last hole, closest to the transom.

 

[rickdb1boat]

Re: "Dolfin motion"

Sounds like you may have a wight distribution problem. Try moving some weight up front and see if that helps. If nessesary, use a couple bags of sand or a couple of people up front and see how it reacts. Did you check the cavitation plates as suggested before. Very critical for proper running at high speed. BTW- You are overreving those motors at 6500 RPMs. I would not run any more than 5800 on those Mariners. You may be exceededing the boats speed design capacity, accounting for the bouncing...

 

[tylerin]

Re: "Dolfin motion"

Maybe just look into some trim tabs, might be all you need

 

[MarkAB]

Re: "Dolfin motion"

"Bokke is Baas"<br />I suggest check RB's post first. Even a 5cm difference in height can have a huge impact. I also had this problem but fixed it cheaply by adding a hydrofoil. Most guys will recommend smart/trim tabs, but they are so expensive here. Are you based in JHB? I know some guys that will assist in boat set up for a small fee at Germiston Lake. This takes out the frustration of trial and error and may save you a few cents.

 

[Jet Blitz]

Re: "Dolfin motion"

Hi Guys,<br /><br />Haven't had an opportunity to check the cavitation plates yet. Will do and let you knoiw. Piet do you have a contact No. for the guy in Germiston?

 

[Jet Blitz]

Re: "Dolfin motion"

Sorry MarkAB I ment to ask you for the number of the guy in Germiston

 

[Jdeagro]

Re: "Dolfin motion"

MarkAB and Jetblitz;<br /><br />You mentioned that the Smart Tabs are very expensive in South Africa. Maybe we can help.<br />Where are you attempting to purchase them and at what price. Contact us through WWW.Nauticusinc.com or www.smarttabs.net.

 

[DJ]

Re: "Dolfin motion"

The motion you describe is called "porpoising". It is typically caused by having to much weight aft.<br /><br />If weight cannot be redistributed, trim tabs will usually correct it.

 

[MarkAB]

Re: "Dolfin motion"

Try Ian @ 869-0408 or Allan @ 455-4046.<br /><br />Nautijohn<br />I will revert via site.

 

[Jet Blitz]

Re: "Dolfin motion"

Hi Guys, Cavitation plates are fine. Level to the lowest point of the V at the back. I am starting to convince myself that weight distribution is the problem. I will keep you updated.<br /><br />MarkAB, Thanks for phone nr's.<br /><br />Hamba Pambilli!