Birchwood 25 - Volvo Penta 145 question

[plumpton]

Hi all. Got a question for those Birchwood 25 owners out there with a Volvo Penta 145 engine...

What kind of speed do you get out of yours? The original sales brochure says 20mph (17 knots). Im only able to get 8-9 knots out of my boat and am working through the engine to try to get to the bottom of the missing horse power.

Would be interested in hearing from other owners out there with the same boat/engine...

 

[Ramage]

When was it last lifted,scrubbed and antifouled? Underwater growth can have a major effect on performance.

 

[plumpton]

We bought the boat in May. We had it lifted then and the hulll was clean having only been antifowled last year.

 

[apollo]

Its not called sandpiper by any chance?

 

[plumpton]

No. used to be called largus. Have you owned a 25 with a Volvo penta 145 by any chance?

 

[scottie]

Are you shure of engine type?

Twin carb hoc with heat exchanger ?

Not single carb ohv raw water cooled as fitted Volvo 145 estate car which would give lower speed?

 

[plumpton]

Yep. That's the one. 2 x solex carbs, hoc with heat exchanger.

Volvo penta 145a.

 

[mlines]

Is it the engine? Has it gained lots of weight in terms on "must haves" or "just in cases" stored on board taking the laden weight up, or even the hull etc absorbing water. Next time its lifted see if you can get a weight reading from the crane operator.

 

[rosssavage]

Ok, to find missing horses, first determine if they're missing!

1) does the engine run at the maximum rated rpm at WOT?

2) is the correct prop fitted?

If: 1)=yes and 2)=yes, then problem is not with engine

If: 1)=yes and 2)=no, then fit correct prop.

If: 1)=no and 2)=yes, then problem is with engine or boat loading/hull condition. See mlines response above for loading/weight issues - it is fair to discount hull condition if it as clean as you believe it is.... Once you've discounted hull and loading, you need to start looking at the engine.

As an aside, if it hasn't been done already, fit electronic ignition.

That's your starting point...

 

[plumpton]

Don't think weight is a major contributor. I've only had the boat 4 months and it's not loaded right up with rubbish yet.

Max rpm is currently 2800rpm. The service guide for the engine suggests around 4200 rpm.

Interesting that the prop has been mentioned. I have had the prop off to try and read the markings on the hub to confirm size and pitch but I couldn't read them unfortunately. I am borrowing a 15" prop off another boat owner tomorrow to compare with the prop fitted to my leg. It's possible that the prop is oversized and may be non original due to the age of the boat.

I have not converted to electronic ignition yet but have new plugs, points, rotor arm, cap and leads fitted so I believe they can be eliminated.

 

[Medskipper]

I owned a Birchwood 25 for about ten years a long time ago. Nobody here yet has mentioned hull type!
The Birchwood 25 was built with a tunnel drive type hull and also a planning hull. If you have the planning hull and trim tabs you should be able to plane the boat, but as others have said it is getting on in years and hulls do soak up water making it heavy.

 

[scottie]

If the boat has been used inland and subject to speed limits it is possible that it has been deliberately over propped

 

[duncan99210]

Whereabouts are you keeping the boat? If it's in sea water and a relatively high fouling area, then you may find that there's significant fouling built up on the hull despite having had it anti fouled in May. We used to find that we needed to scrub the hull mid way through the season when we kept our mobo in the Menai Straits. Might be worth checking before going too far down any other routes, or has the performance been a problem since anti foul was put on?

 

[ms1]

you do need engine RPM
you dont say if your 2800 is in or out of drive
if OUT then engine is not producing enough RPM, clearly
if IN, then someone may have fitted an oversize Prop trying, unsuccessfully, to get more speed and thus preventing the engine winding up to its high RPM.

sometimes owners will REDUCE their prop size for easier handling on non tidal waters, so if you get high RPM but still no speed this might be the reason.
Guessing here but original factory prop might be something like 15x17
15 being diameter
17 being 'pitch'
a larger dia prop wont necessarily do anything to help you because pitch is prob the major component in speed.

If its a Volvo 270 or 280 leg then I think a 16 x 23 is the largest prop it will take but I doubt whether a 145HP will swing that.
dia goes down inch by inch 16,15,14 etc
pitch goes down in 2's 23,21,19,17 etc

I hope you get to the bottom of it.

 

[plumpton]

Thanks for all the replies everyone. The engine is revving fine in neutral. I have been loaned a prop from a chap that also has VP145's on 280 outdrives. He says its a standard size but dont know what it is until I pick it up this weekend.

Im sure its prop related because the hull is clean, the engine has been well serviced by me and things like spark plug colour are healthy so its firing nicely. The boat is also not over stocked with rubbish. We only have a few supplies, some cutlery, 18 gallons (approx) of fuel and a tank of water up the front.

I hope to pop the loan prop on this weekend and find out once and for all whats going on.

Im really hoping that another Birchwood 25 owner with the same engine configuration will find this thread and tell me what they get from their 25 at full throttle...

 

[Chris_d]

I would prepare to be disappointed, suspect that old brochure speed was optimistic and was achieved with a factory fresh empty boat with no antifouling just dropped in for the speed trial. The rule of thumb for a planning boat is minimum 60hp/ton to get up on the plane so 145hp (probably actually more like 130hp) is going to be very marginal even if everything is perfect, suspect your clean bottom is not as clean as you think and if achieving 8/9 knots that is the point where the bow starts to lift and you should be climbing over the bow wave. If there is any drag from some slim or weed, excess weight, that is as fast you will go. Do you have trim tabs? they will need to be fully down and the leg trimmed right in to get it up, if it does start to plane it will go to a minimum planning speed of about 14knots, drop any lower then it will fall off the plane back to 8knots again. You cannot do any speed in between its either planning or not planning, so suspect its just underpowered. Believe Birchwood did a version with twin 145's for just over 20knts but it wasn't very common.

 

[No Regrets]

It's probably a combination of the 40 year old engine having lost a little power (Although engines can actually improve with age to a point!) and the boat having become heavier than standard spec with options added over the years, hull moisture etc.

Its likely to have Osmotic blisters too, which don't help.

A good tune up (Carbs and timing, valve adjustments) and a damn good thrashing should see it plane though, assuming any extra weight has been removed, and after an hour at full blast to clear all the cobwebs it'll be better next time you use it. Sometimes having a passenger run down to the front might help kick the stern up if it's marginal!

 

[apollo]

I used to have a Birchwood 25 Interceptor with a 130Hp Volvo Petrol and that would plane no problem. But that boat didn't have any junk on it and i had the right prop.

2800rpm does indicate you are massively over propped.

I am estimating something like a 14" X 13" prop is about right but it was a long time ago (>20y)

What size prop you got?

I did have a mate with 145hp and his was like yours only 9-10knots.

When he sold it and was delivering it to the new owners just upstream of Kingston with all the years of junk removed, it did finally plane...

 

[plumpton]

I popped the prop off recently to look for the size but the numbers were corroded and covered in crud so i could not read them.

The prop im borrowing is off a fairine 29 with the same engine/leg.

It does sound like I need to speak to someone to work out the correct prop sizing. Does anyone know of a website that can work this out by any chance?

 

[BB1]

Is it off a Fairline 29 with single engine ? I would have thought you should be around 15 X 13.