Volvo Penta D3-130

[gordmac]

Had a quick Google. Are you sure they are meant to use at sea? They seem to also have come with two Mercruiser 120hp engines, I don't think that sort of power is enough for a boat that size.
Sunline 31
Seems they may also have come with twin 160hp d3 engines.

 

[Portofino]

I dont think you can compare your engine to a d3 like that - they are totally different ( as evideenced by your red line at 2150rpm , and the d3 revving to 4100rpm) , and as such the normal range of boost pressure will be vastly different in each engine (as shown in the table above)

True .
Just throwing normal boost p about.It seems low .As said around 1.7/1.8 bar running is very common.Even small petrols Fiat uno , Renault 5 s etc

 

[Jonathan2021]

How’s the fuel ?

Diesel seems fine. I treat it for diesel bug so that should not be a issue

 

[Jonathan2021]

Does it help moving people forward?

My setup does not really allow much movement of people forward and I have done all I can to move things towards the bow.
Other than the engines and battery’s the engine bay is empty of all necessary items

 

[julians]

My setup does not really allow much movement of people forward and I have done all I can to move things towards the bow.
Other than the engines and battery’s the engine bay is empty of all necessary items

It may simply be underpowered in that case , you say that once on the plane it hits the max rated rpm of the engines, so its not a propping or fouling issue I would guess.

Do you know the all up weight of the boat in its current state with all the people ,gear and fuel on board?

260hp is not a lot for a boat that size

 

[Jonathan2021]

Had a quick Google. Are you sure they are meant to use at sea? They seem to also have come with two Mercruiser 120hp engines, I don't think that sort of power is enough for a boat that size.
Sunline 31
Seems they may also have come with twin 160hp d3 engines.

I am indeed wondering if my set up was intended for more a river cruiser rather than sea.
It’s the correct class for sea and I have known other others on the sea but I do not know what engines they were running

 

[Jonathan2021]

It may simply be underpowered in that case , you say that once on the plane it hits the max rated rpm of the engines, so its not a propping or fouling issue I would guess.

Do you know the all up weight of the boat in its current state with all the people ,gear and fuel on board?

260hp is not a lot for a boat that size

Fully loaded its 3490 k

It may simply be underpowered in that case , you say that once on the plane it hits the max rated rpm of the engines, so its not a propping or fouling issue I would guess.

Do you know the all up weight of the boat in its current state with all the people ,gear and fuel on board?

260hp is not a lot for a boat that size

its 3450kgs fully loaded people, fuel, water etc

 

[Jonathan2021]

Have the props been changed ? Your way down on rpms there. Should be 3800-4000ish I think.
edit...those rpms are for the 190..apologies. the 130 will be less rpm for sure

My first initial thoughts were that it may be over propped but I cant find any owners of the same bought for comparison to

 

[julians]

Fully loaded its 3490 k

its 3450kgs fully loaded people, fuel, water etc

that sounds lighter than I would have expected - a lot of other ads for sunline 31's say the weight is more like 4500kg. Either way it a lot of weight for not much power.

 

[julians]

My first initial thoughts were that it may be over propped but I cant find any owners of the same bought for comparison to

you said in your original post that you hit 4000rpm when you get it planing - which implies the props are ok - I think

 

[Jonathan2021]

you said in your original post that you hit 4000rpm when you get it planing - which implies the props are ok - I think

I originally wondered if a different type of prop would give me more lift but after reading it seems that the 4 blade props it has is as good as it gets (according to google)

 

[julians]

it sounds like trim tabs could help - but its a relatively expensive thing to try if it doesnt make a significant difference.

 

[SC35]

"WOT is 3000rpm with 14.5 psi but once on the plane it revs to 4000rpm happily"

The problem is that beyond 3000rpm, the torque curve of this engine is falling away.
So if this corresponds with the "hump" speed, it will take a long time to get over it, if at all.

Ideally a boat will be fully on the plane before the torque drops off in the upper reaches of the speed range.

 

[Jonathan2021]

it sounds like trim tabs could help - but its a relatively expensive thing to try if it doesnt make a significant difference.

I may just have to swallow the risk and cost. Bennet trim tabs seem popular. I sense another Googling session coming “best trim tabs”

 

[Jonathan2021]

"WOT is 3000rpm with 14.5 psi but once on the plane it revs to 4000rpm happily"

The problem is that beyond 3000rpm, the torque curve of this engine is falling away.
So if this corresponds with the "hump" speed, it will take a long time to get over it, if at all.

Ideally a boat will be fully on the plane before the torque drops off in the upper reaches of the speed range.


View attachment 132856

Hmm that’s very valid and the problem in a nut shell

 

[SC35]

Hmm that’s very valid and the problem in a nut shell

An interesting experiment would be to try one size larger props, but practically, it's difficult to "borrow" props and buying them would be an expensive experiment, unless you can find someone else with a similar boat that has the same setup.

 

[julians]

I may just have to swallow the risk and cost. Bennet trim tabs seem popular. I sense another Googling session coming “best trim tabs”

yep, my previous boat had bennet trim tabs - they never went wrong in 15 years - totally bullet proof reliability in my experience

 

[SC35]

yep, my previous boat had bennet trim tabs - they never went wrong in 15 years - totally bullet proof reliability in my experience

Worth a try, I think: the additional "lift" from the stern could tip things over the edge in your favour.

 

[Jonathan2021]

Worth a try, I think: the additional "lift" from the stern could tip things over the edge in your favour.

Yes I’m beginning to get that impression. I will keep you posted

 

[julians]

Yes I’m beginning to get that impression. I will keep you posted

have a look at smart tabs - google them.

I've never used them, but a lot of people (admittedly with smaller boats) swear by them for improving planing behaviour .

They're like trim tabs, but they're not controllable by the driver, they are mounted on some passive some spring rams that allow them to constantly apply an amount of pressure. They're cheaper than regular trim tabs as a result, but less useful too (ie they cant compensate for uneven port to starboard loads)