Trimming not going to plan.

[Gosub]

Hi People.
I've read a ton of threads on here about how you trim up until she porpoises and then trim back a bit. That sounds simple enough. My Monterey 236 (Merc 5.7 alpha 1) planes nicely and I can feel it going faster as I trim it up. But... when I reach a certain point the boat just bogs and the revs go up (cavitating?). No sign of a porpoise anywhere. It just dies until I get the trim back down to where it's happier then I can trim back up a bit. Is this just another way of behaving or am I doing something wrong.

This is on a calm Mediterranean sea if that has any bearing. Oh and no trim tabs.


Cheers
Steve.

 

[Maclin]

Re: Trimming not going to plan.

The advice should read more like ..."trim up until she porpoises or the prop blows out and then trim back a bit"...

 

[tpenfield]

Re: Trimming not going to plan.

Some boats will not do the porpoise thing, others will. You ventilated the prop by trimming up too far.

You only want to trim it to the point where you notice a little bit of speed and RPM increase, then stop trimming and enjoy the ride.

 

[Philster]

Re: Trimming not going to plan.

Hi People.
But... when I reach a certain point the boat just bogs and the revs go up (cavitating?). No sign of a porpoise anywhere. It just dies until I get the trim back down to where it's happier then I can trim back up a bit. Is this just another way of behaving or am I doing something wrong.




Cheers
Steve.

Yeah, trimming til she loses bite and ventilates: Don't do that?!

Some boats will porpoise before that ever happens; some won't. But now you have a good idea of how far is too far. Do you have a trim gauge?

 

[bruceb58]

Re: Trimming not going to plan.

Trim in small steps and let everything equilize before you trim again. Depending on the size of your boat. you can trim way faster than the boat can react.

 

[90stingray]

Re: Trimming not going to plan.

My Stingray would porpoise and chine walk when at the max trim you should be trimming. The Glastron blows out when trimmed too much. Differnet hulls act differently as stated. Trim on friend....

 

[shrew]

Re: Trimming not going to plan.

Does your boat also have trim tabs of any kind? (smart tabs, electric, hydraulic?) This also will dictate how you trim the outdrive. Tabs will bring the bow back down again. Which will actually trim the outdrive further out, technically speaking. The idea is that the drive should essentially be verticle, with the prop thrust pushing backwards as opposed to back and up or back and down. The amount you trim the drive out is really based more on the running angle of the hull. The more you use tab IN to bring the bow down, the less you need to trim the drive OUT. I more closely watch the RPM's. When I no longer see an appreciable change in RPM or speed, it's about right. And once you seee either porpoising OR you that tell tale ventilation sound, trim the drive IN until either stops.

 

[Gosub]

Re: Trimming not going to plan.

Thanks for the replies guys. Now I know it's normal I'll get used to it and trim accordingly.

No trim tabs. I does have a trim meter, but that doesn't give an accurate reading of how the drive is trimmed. It's either full in or full out according to it. Probably something wrong there.

 

[Bondo]

Re: Trimming not going to plan.

I does have a trim meter, but that doesn't give an accurate reading of how the drive is trimmed. It's either full in or full out according to it. Probably something wrong there.

Ayuh,.... it's 'bout the most useless gauge ever put in a boat anyways,...

The seat of yer pants is a Better gauge, 'n more reliable...

 

[Philster]

Re: Trimming not going to plan.

Well that's begging the question.

Don't get a gauge because seat of yer pantaloons is 'better' and 'more reliable'.

Everyone can boat by the seat of the pants, so a trim gauge is the most useless. Wait, maybe we just have a flawed premise there. I think it's safer to say that there are some boaters who would be well-suited to have a trim gauge as a guideline, and that if they should develop a seat-of-yer pants feel over time, they can depend on that feel more.

Based on many questions offered here, there are boaters who would not find the trim gauge to be useless.

 

[JoLin]

Re: Trimming not going to plan.

Well that's begging the question.

Don't get a gauge because seat of yer pantaloons is 'better' and 'more reliable'.

Everyone can boat by the seat of the pants, so a trim gauge is the most useless. Wait, maybe we just have a flawed premise there. I think it's safer to say that there are some boaters who would be well-suited to have a trim gauge as a guideline, and that if they should develop a seat-of-yer pants feel over time, they can depend on that feel more.

Based on many questions offered here, there are boaters who would not find the trim gauge to be useless.

I made a point this year of having the outdrive trim indicators fixed, simply so I'll know if they're both tilted in the same ballpark. I never needed it with a single engine, but between the Bennetts and the dual outdrive trims, I can have a tough time just knowing where everything's situated. Maybe I haven't sufficiently developed the 'seat of the pants' feel yet...

 

[tpenfield]

Re: Trimming not going to plan.

The regular trim indicator gauges are a bit sloppy, but I find a use for it at the beginning and end of each outing on the boat. It tells me when I have got the outdrive down to a reasonable level when I start out, and tells me when I have the outdrive up to my preferred up position at the end of the day.

For actual 'trim' of the outdrive while underway, I have a mechanical indicator, which gives a very precise position of the outdrive.

 

[ezmobee]

Re: Trimming not going to plan.

If the OP's boat is heavy and/or has a good amount weight in the front, it may never porpoise.

Based on many questions offered here, there are boaters who would not find the trim gauge to be useless.

My trim gauge reads backwards (stupid OMC vs. Merc compatibilities) so it's fairly useless :facepalm:

 

[bruceb58]

Re: Trimming not going to plan.

If the OP's boat is heavy and/or has a good amount weight in the front, it may never porpoise.




My trim gauge reads backwards (stupid OMC vs. Merc compatibilities) so it's fairly useless :facepalm:

Its pretty easy to make it work properly if its a 3 wire sender.

I repaired my trim gauge by replacing the sender when I bought my boat. When it goes out again, I won't bother. I agree its pretty useless.

 

[Philster]

Re: Trimming not going to plan.

If the OP's boat is heavy and/or has a good amount weight in the front, it may never porpoise.

My trim gauge reads backwards (stupid OMC vs. Merc compatibilities) so it's fairly useless :facepalm:

:facepalm:

 

[ezmobee]

Re: Trimming not going to plan.

Its pretty easy to make it work properly if its a 3 wire sender.

It's just a two wire resistance measuring thing I believe. Tough to reverse that.

 

[bruceb58]

Re: Trimming not going to plan.

It's just a two wire resistance measuring thing I believe. Tough to reverse that.

On my Volvo sender there are three wires and you just pick the proper 2.