I asked before - but never really got full answer .. outdrive leg tilt limit pin.

Refueler

Refueler

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My AQ270 outdrive leg has the limit pin 0ne hole out from most fwd ... the leg appears to be a slight bit prop angled back from vertical.

drive angle.jpg

Angle there exxagerated ... its actually barely visible ...

The boat bow rises very easily as throttle increased and can chine ride at slightest provocation ... the trim tabs do work - but its a delicate op using them. They have no position indication.

I'm wondering if I move the leg to the red line veritcal would this help ?? or make it worse ?
 
Sorry I have to disagree with simonfraser, true it lifts the bow but thats not what you need starting from rest as the hull presents its worst angle of attack just when you are trying to accelerate the hull to its planing speed. Its proven that you trim full in to get on the plane quickly letting the hull run flat until it generates enough lift to climb on the plane, then you trim out to find the sweet spot for best speed or handling depending on the sea conditions. I know this works having tested everything from many types of weekend cruisers to all Hydrolift and Goldfish boats and especially on the two 120 knot+ Nortech catamarans I maintained.
I don’t know what boat you have Refueler, chine walk is usually a sign its trimmed too high so I would try it further in it can’t hurt and just see if it performs better in any way, and the rule of thumb is use as little trim tab as possible as they also cause uneccessary drag.
 
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One of the problems is that the boat originally had the B20 Volvo Penta 4cyl engine (130HP) ... owner before me swapped it out for the B30 6cyl engine (170HP) ... so she sits down by stern when at rest ..
I'm planning to fill the watertank up in the bow .. try to get that bow down and a better presentation waterline ...

If there are 4 people on board with 2 sitting on the aft bench .. the fuel consumption goes through the roof, engine doesn't want to rev high and I have real trouble getting bow down to get on plane ...
 
That is one thirsty engine, I remember them from when I was a Volvo car mechanic and also in the marine branch. From what you say you need to try the inner position for the tilt pin, does the engine reach the correct WOT rpm as if its overpropped that won’t help either.
 
spannerman said:
That is one thirsty engine, I remember them from when I was a Volvo car mechanic and also in the marine branch. From what you say you need to try the inner position for the tilt pin, does the engine reach the correct WOT rpm as if its overpropped that won’t help either.
Click to expand...

According to the gauge - she revs fine when boat planes .... but when I have people in cockpit and stern sits down ... she finds it hard to rev .. If I get someone to go fwd and sit on deck .. then bow goes down and she revs better.

The drive / prop is correct for the engine ....

Outdrive is standard AQ270 ... for the VP AQ170 6cyl.

If I run her alone or 2 up ... she averages 15lt/hr for 15kts .... push her to 24kts and she burns 26 - 28lt/hr.
If I have 4 people on board and all in cockpit ... I get 20lt/hr for 12kts !! and hard to get past 14kts ..
 
I have 2 ton Draco 24ft with a 5,7ltr 260hp V8. At 24 knts it uses 38lt/hr at 3000rpm if I take it to max 36knts at 4500rpm its 70lt/hr, so guess what speed I drive at!
 
Refueler said:
According to the gauge - she revs fine when boat planes .... but when I have people in cockpit and stern sits down ... she finds it hard to rev .. If I get someone to go fwd and sit on deck .. then bow goes down and she revs better.

The drive / prop is correct for the engine ....
Click to expand...

That is a very classical sign of an underpowered boat when she only gets on plane when somebody moves fwd or you ride alone . With passengers onboard you then do not fully plane but plow thru the water with an awful fuel consumption.

I also cannot imagine you have chine walking . Chine walking is side to side rocking at very high speeds , something usually found in very high powered boats .

What you may have is somekind of bowsurfing because you try push the bow down to much in a try to overcome the lack of power . In this case the boat might have a tendency to list and/or veer off course .
 
The boat was designed for the 13hp B20 VP .... and the sales photos show her planing well ... (she is a one-off boat though).

Previous owner swapped out the lighter B20 for the heavy B30 engine and leg ... I don't think was a good idea. It makes the boat sit down and aft ...

Here she is before engine change :

Primor B20.jpg

You can see she's reasonable level ....

Here she is now with the B30 and visibly not level ! ...

Primor at home 13 Oct 2025 (1).jpg

And a stern shot showing the outdrive near full submerged ! ...

Primor at home 13 Oct 2025 (2).jpg

Its why I think filling the water tank in the bow might help ....
 
Refueler said:
The boat was designed for the 13hp B20 VP .... and the sales photos show her planing well ... (she is a one-off boat though).

Previous owner swapped out the lighter B20 for the heavy B30 engine and leg ... I don't think was a good idea. It makes the boat sit down and aft ...

Here she is before engine change :

View attachment 208530

You can see she's reasonable level ....

Here she is now with the B30 and visibly not level ! ...

View attachment 208532

And a stern shot showing the outdrive near full submerged ! ...

View attachment 208533

Its why I think filling the water tank in the bow might help ....
Click to expand...
Next winters project. Move the engine forward.

A few bits of timber for the engine mounts and a bit of scaffold tube to extend the drive shaft ......
 
Boathook said:
Next winters project. Move the engine forward.

A few bits of timber for the engine mounts and a bit of scaffold tube to extend the drive shaft ......
Click to expand...

The only way to do that ... would be to cut into the cabin via the aft bulkhead.

I'd put back a B20 engine - but it means outdrive change as well ... or prop at least.

Whatever - would be a major job.

Matter of coming to terms with the present setup ..
 
Refueler said:
The only way to do that ... would be to cut into the cabin via the aft bulkhead.

I'd put back a B20 engine - but it means outdrive change as well ... or prop at least.

Whatever - would be a major job.

Matter of coming to terms with the present setup ..
Click to expand...
Are you able to move the aft bench forward so people are not sitting right at the stern ?

Easiest option is to accept existing setup and resign yourself to travelling at a much slower speed, 8 to 10 knots, with guests
 
Aft bench ... not really as I will be changing the fixed helm / frone guest seats (they are 4 leg fixed frame hinged to cockpit sides) to pedestal swivel seats .. and small hinged table each side between fwd and aft seats.
The run at lower speed is about the only option really ...

It does seem to be strange though ... I had 5 on board one time ... and she ran fine ... then a later run with 4 and she was terrible ...
 
Refueler said:
The boat was designed for the 13hp B20 VP .... and the sales photos show her planing well ... (she is a one-off boat though).

Previous owner swapped out the lighter B20 for the heavy B30 engine and leg ... I don't think was a good idea. It makes the boat sit down and aft ...

Here she is before engine change :

View attachment 208530

You can see she's reasonable level ....

Here she is now with the B30 and visibly not level ! ...

View attachment 208532
Click to expand...

Nice boat !

When you plane out alone and the engine reaches ~ rated revs but struggle to get on plane with passengers there is no rocket science - the engine simply lacks power for the given boat .

Of course the b30 makes the boat more ass heavy but on the other hand should be significantly more powerful comparing to the b20 .

Try a planeout with tabs down but immediately fully rise them after "take off" .

If you have bowsurfing already i,m afraid it gets worse when you shift weight to the front , but try .
 
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