Boat doen't run right with motor trim angle

H

Higgins79

Seaman Apprentice
Joined
Jul 19, 2012
Messages
35
Hey y'all. I have a 40hp longshaft Nissan on my 1648 Landau mod V bottom. I'm having some issue controlling the boat. The boat dry only weighs 250lbs, and I think that may be the problem. The trim notch I run it at currently makes the boat porpoise too much, but if I trim it down, the motor drags through the water too much. There is no trim angle between these 2 notches and I'm wondering what to do. The boat runs fine with 2 people at the higher trim. Is adding weight the only way to solve this? I'm getting about 30mph with 2 people but I'd like more speed! I also plan on getting a lower pith prop because the current pitch is 14", which I think is made more for torque. Props range from 16 to 7 for this motor. What would be a good one to get? I appreciate any advice.
 
M

Maclin

Admiral
Joined
May 27, 2007
Messages
6,761
Re: Boat doen't run right with motor trim angle

Look into Smart Tabs from Nauticus Inc. They have some for small boats that may just be the ticket for your condition. I think I can give the web site with no conflict of interest, you can buy them thru iBoats.


SMART TABS raise your performance expectations.
 
smokeonthewater

smokeonthewater

Fleet Admiral
Joined
Dec 3, 2009
Messages
9,838
Re: Boat doen't run right with motor trim angle

there are lots of variables not mentioned...

is the motor the right length for the boat? the anti ventilation plate should be even with the bottom of the keel or slightly above

what rpm's are you running at full throttle?

have you moved all possible weight forward? batt(s), fuel tank, anchor, cooler

do you have a hydrofoil on the engine? if so try removing it

is there any damage to the bottom of your boat? dented, warped

is your prop in good condition?

how is your holeshot?
 
roscoe

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,665
Re: Boat doen't run right with motor trim angle

getting a lower pitch prop will create more torque and rpm, less speed.
 
H

Higgins79

Seaman Apprentice
Joined
Jul 19, 2012
Messages
35
Re: Boat doen't run right with motor trim angle

The motor is the right length, the hull and holeshot are fine and there is no hydrofoil. I can move stuff towards the front but other than the battery I usually don't carry much heavy stuff. I don't have a way of measuring rpm but the previous owner told me that he had a high torque prop with pitch 14 because he had it on a 600+ pound boat. The prop itself doesn't have a number on it so maybe the guy was wrong.
 
H

Higgins79

Seaman Apprentice
Joined
Jul 19, 2012
Messages
35
Re: Boat doen't run right with motor trim angle

When I said the holeshot was fine I meant that the boat literally take no effort to plane. It plane at low rpm at maybe 1/4 throttle. The motor is a bit overpowered for such a light boat... (problem?) haha the boat is only rated for 30hp
 
Alumarine

Alumarine

Captain
Joined
Feb 22, 2005
Messages
3,693
Re: Boat doen't run right with motor trim angle

What does "the motor drags through the water too much" mean?
 
H

Higgins79

Seaman Apprentice
Joined
Jul 19, 2012
Messages
35
Re: Boat doen't run right with motor trim angle

The motor creates drag and water sprays both into the boat and onto the motor cowling. It also becomes really stubborn to steer
 
H

Higgins79

Seaman Apprentice
Joined
Jul 19, 2012
Messages
35
Re: Boat doesn't run right with motor trim angle

Re: Boat doesn't run right with motor trim angle

Yeah... my rig is just ****ed up in general. With me and the battery in the back and about 80lbs of another battery and an anchor in the front it still runs a bit "off". I need my fatass friend up front to make it run smooth
 
EddiePetty

EddiePetty

Lieutenant Junior Grade
Joined
Aug 25, 2008
Messages
1,008
Re: Boat doesn't run right with motor trim angle

Re: Boat doesn't run right with motor trim angle

I was looking at some pictures of 1648 Landaus on the net and I swear I cannot see one needing a long shaft engine.

Please post a picture of the rig from the side showing the relationship of the ventilation plate to the hull, and provide the scale dimension from the top of the transom cut-out to the bottom of the hull.

Me thinks ya' got too much motor in the water! :)
 
smokeonthewater

smokeonthewater

Fleet Admiral
Joined
Dec 3, 2009
Messages
9,838
Re: Boat doesn't run right with motor trim angle

Re: Boat doesn't run right with motor trim angle

I think so too....
 
JimS123

JimS123

Fleet Admiral
Joined
Jul 27, 2007
Messages
7,981
Re: Boat doesn't run right with motor trim angle

Re: Boat doesn't run right with motor trim angle

Higgins79 said:
Yeah... my rig is just ****ed up in general. With me and the battery in the back and about 80lbs of another battery and an anchor in the front it still runs a bit "off". I need my fatass friend up front to make it run smooth
Click to expand...

It has nothing to do with your friend or the equipment in it. The only thing ****** up about it is the size of the motor. It's unsafe and dangerous to be on the water. That's a little boat and a big engine. You need to trade the motor in for a 25.
 
jestor68

jestor68

Commander
Joined
Jun 12, 2012
Messages
2,308
Re: Boat doesn't run right with motor trim angle

Re: Boat doesn't run right with motor trim angle

The difference in weight between the Nissan 30 and 40 is only about 25-30 lbs, so weight shouldn't be the issue.

We have determined from another thread ongoing on the prop forum that transom height is OK.

A forty and a boat rated for 30 is not necessarily a safety issue, since the builders usually include a fudge factor in their power ratings. If you ran the CG formula on his boat, I'd bet you'd come up a 40 hp rating(or better).

So, I am going to suggest you try a "Doel Fin" to solve your porpoising/handling issues. 00440.jpg It has worked for thousands of others with boats in your size and category. I have personally used it on a couple of boats, and it did in fact work as advertised. I call it the forty dollar wonder. :)
 
JimS123

JimS123

Fleet Admiral
Joined
Jul 27, 2007
Messages
7,981
Re: Boat doesn't run right with motor trim angle

Re: Boat doesn't run right with motor trim angle

jestor68 said:
The difference in weight between the Nissan 30 and 40 is only about 25-30 lbs, so weight shouldn't be the issue.

We have determined from another thread ongoing on the prop forum that transom height is OK.

A forty and a boat rated for 30 is not necessarily a safety issue, since the builders usually include a fudge factor in their power ratings. If you ran the CG formula on his boat, I'd bet you'd come up a 40 hp rating(or better).

So, I am going to suggest you try a "Doel Fin" to solve your porpoising/handling issues. View attachment 174826 It has worked for thousands of others with boats in your size and category. I have personally used it on a couple of boats, and it did in fact work as advertised. I call it the forty dollar wonder. :)
Click to expand...

Real bad advice regarding HP. Hope no ambulance chasing lawyers are following waiting for an accident to happen.

Personally, I think a DoelFin is better than sliced bread. In fact most every boat in the family has one. My personal experience dates back to when they were first invented, almost 30 years ago. Fantastic add-on for an under-powered boat.

Howsoever.......a Doelfin on an overpowered boat could be more dangerous than the over-powering itself.
 
M

Mi duckdown

Commander
Joined
Apr 14, 2007
Messages
2,575
Re: Boat doesn't run right with motor trim angle

Re: Boat doesn't run right with motor trim angle

Need to show Pics of motor/transom setup. I guessing longshaft motor on 15 inch transom.???
 
You must log in or register to reply here.
Top