Boat porpoising

[Trains1938]

I people, I just bought a 17' Star craft open bow boat. Took it out and I found out that it wants to porpoise (bow bounces up and down) when it plans out. It has a 65 hp Johnson motor. What can be done to fix this? Anybody have a idea. Trains1938

 

[Pete_a]

Trim outboard it down a touch. Youtube some how to trim a boat videos

 

[alldodge]

You do want to trim it in more, and if you don't have power trim pull the pin out on the transom and reinstall one hole closer to the boat

 

[fhhuber]

If its really close... just moving weight forward might fix it.

 

[Watermann]

That's a common problem when the stern is heavy and the bow is light. As said above dropping the thrust bar down and re-positioning some of the weight forward in the boat should help out with the porpoising issue. If not trim tabs might be a good choice for pushing the bow down and lifting the stern.

 

[Trains1938]

Hi guys, The motor is already as low as it can get. What is a good source for the trim tabs and how big should they be? Thanks for the come back trains1938

 

[sphelps]

Here ya go .. http://www.iboats.com/Nauticus-SX-S...1871692--session_id.780643953--view_id.352485
These may help ... I have them on my boat but it did not completely stop the porpoising although it did help .. I figured out that I did not have enough transom angle so I installed transom wedges on the motor bracket ... Completely solved the problem ,,,

 

[Watermann]

I use the Nauticus smart tabs that I got here at iboats. The ones in the link are what I bought but they have a bunch of different options like color and material. Take a look at thier video and see if it's something that would help out with your boat.

 

[alldodge]

Can you post a pic of the transom and motor?

 

[Teamster]

What is your gps speed and engine rpm's?

A drop in pitch might fix it,...

Sometimes moving the motor up can fix it as well,...

 

[redneck joe]

Doesnt too long of a shaft contribute?


And before adding tabs, start with moving weight around

 

[White90GT]

I was going to suggest putting weight in the bow. I actually have 90 lbs worth of weight in the anchor locker on my 17' chris Craft I/O.

 

[Trains1938]

No Title

AllDodge, Here is the pic. you requested. Trains1938

 

[Trains1938]

Hi Teamster, Don't know the answer to your questions. I don't have a gps or a tac in the boat. Don't know what the pitch is on the prop. where would that be stamped?

 

[Watermann]

I have a couple questions about the pic you posted. I'm wondering what that odd looking pin is doing in the outer most hole? What is the purpose of the rope and carabiner under the mount?

I also have a suggestion for you. See that rusted looking washer on the motor mount bolt, that is not factory so someone has pulled that bolt, maybe lost the stainless washer and put that steel one on there. My worry is that whoever would do that would also not use a proper sealant when replacing the bolt. That is a sure way to cause the wood transom to start rotting and the steel to start corrosion.

 

[Patfromny]

I agree with watermann. Also, it seems the engine is as low as it can get on that bolt and rusty washer. It is probably too low. Seeing the gold color im guessing you have a 78ish evinrude. This is the same year engine i had on my boat and i had it about an inch or so higher than yours is now. Could you post a pic of the whole engine and back of boat. Maybe from the side? Seeing the relationship between engine height and boat could solve your whole problem. You want the cavitation plate at least even with the bottom of the hulls lowest point. Maybe even an inch or 2 above that point but a good start would be even with the bottom. This will help with proposing as well as trimming the motor. You want the engine pushing while level with the boat. Once you get the engine height set, try moving that pin up a position at a time until the boat slows down, then back off a pin. You def. Want an equal distribution of weight. More to bow is probably better than more to stern. Hope this helps.

 

[alldodge]

Thanks for the pic, and sorry I should have explained a bit more. I was wanting to see the entire transom to see how the motor lines up with hull. As another mentioned, to see if the shaft length looks correct.

 

[redneck joe]

i love it when I do a google search and the top results are here on iboats...

 

[redneck joe]

and this

 

[Trains1938]

Hi Watermann, 1.The odd looking pin is a bracket that will hinge up to support the motor during transport. 2.The white rope is there to lift the bracket into place when you raise the motor. I plan to replace the bolt and washer as soon as I get to town and get one.