Albin 25: Emergency Propulsion/Kicker Motor

[Cappuccino]

These are my original questions:
"
1) Will I be able to hit say 10 to 12 knots with this setup?
2) Will the extra 25hp of the outboard plus the 33hp of the diesel be enough to get to 10 to 12 knots?
3) I know that true planning will be impossible or near impossible with that extra horsepower but maybe plane a bit?
4) Will the turbulence of the diesel prop affect too much the prop of the outboard even though they will be both deep enough with no air(no exhaust gases)? And if so, could I reduce the rpms of the diesel enough to make the boat go to a certain speed and use the outboard as a kicker/main power and thus extending the life of the diesel? "

So far basically I've been told so far that the boat is going to squat and that going faster than hull speed is not possible.

Since I found those videos of actual Albin 25's I know for a fact that this hull with enough power is capable of doing 14+ knots.
Squatting, well that is what trim tabs are for or even better an extended hull past beyond the outboard that I am planning to install or even more better the same extended hull with added trim tabs.
I imagine that the next post will be about efficiency and fuel consumption? Not to worry I am not worried about spending a few dollars more when going faster, not a problem.
Not trying to be a jerk but I just need for someone to give me some light on the questions I asked.
I already know that 14+ knots is achiveable.
Thank you

 

[DogCavalry]

@Cappuccino , for a non-planing hull, thr drag increase at the onset of planing is catastrophic. It may be possible to get to 14 knots, but impossible to maintain 10 knots. Boats, even properly designed planing boats regularly have a speed they can't maintain, where the dramatic increase in drag happens at a speed where the prop, limited in rpm at that speed, can't get up into the operating rpm range where the engine can make enough power to maintain that speed. That is experienced as a speed where the boat falls off the plane.

That is a long way of saying, "maybe not" to your original question. It depends on much. What are the numbers on the potential prop on the theoretical supplemental outboard? Maybe you could get a prop optimized for the speed where the extra power is needed.

 

[kapnD]

While the outboards prop may be fine at 14 knots, the inboard’s prop is most likely designed to be optimal at hull speeds, and may not be of any benefit at all if pushed far above that.

 

[seasquirt]

Try contacting the owners of the fast boats and see what they did to get there, eg. have they stripped out the interior to lighten it, made tanks smaller or removed them, re-painted the hull, or other speed tricks. What are the rotations of both props, you plan to use, because with different prop heights, possibly counter rotating may be better than same rotations, and also reduce prop walk, but also may make little difference. If you plan to steer with the OB through a hole, that hole (even in a sealed tube in your extra buoyancy) will cause hull bottom turbulence, and drag, possibly negating your gains. I'm not condoning your idea, I'm with the other replies, but giving you more to weigh up. Search if anyone else has added an OB to a similar hull to augment a displacement diesel setup; If it was a good Idea, then in the last 50 years it possibly would have become popular. You will also need to carry an extra fuel tank, and 2 different fuels, probably.

 

[willy13]

Albin-25 "Displacement" or "Semi-displacement" hull? - Albin Owners Group https://albinowners.net/aog/viewtopic.php?t=5867
It looks like there might be a slight change in aft hull shape to make later Albin 25 into a semi-displacement hull. If this is true, make sure you know which one you have and which one that 14 kt Albin is.

 

[skaraborgcraft]

Later models were fitted with 36hp Volvo triples, over the original Albin 20hp twin.

 

[Cappuccino]

The

Albin-25 "Displacement" or "Semi-displacement" hull? - Albin Owners Group https://albinowners.net/aog/viewtopic.php?t=5867
It looks like there might be a slight change in aft hull shape to make later Albin 25 into a semi-displacement hull. If this is true, make sure you know which one you have and which one that 14 kt Albin is.

Yes, I checked the 14 knot Albin is exactly the same hull as mine.
Later models, the semi-displacement ones, or "Deluxe" were able to hit 10 knots. The early versions like mine are rated at 8 knots which is more or less constant to what we experience in real life sailing.
That's why I truly believe that making the hull extension and copying the form of a semi-displacement design and doing my extension in that matter will help in converting my hull/aft section to a semi-displacement hull, the added water length plus the bouyancy. And if in top of that I add 76% more power with the outboard it might be just the recipe I am looking for.

 

[Cappuccino]

The owner of this Albin 25 bought the boat with this hull extension. The one who did it followed the lines of the boat thus my guess is that he kept the aft design as a displacement hull???
My thinking is, and please correct me if I am wrong, is that in order to achieve a semi-displacement hull the end of the extension should not be rounded and it must end in a sharp edge like most planning hulls. Also it should be more flattened, correct??

This picture is an example of how I intend to make the swimming platform extension and how the outboard is going to be hidden behind the steps. This is an example, not exactly how I intend to do it.

 

[Cappuccino]

This more or less what I want to achieve. Hidden in the stair box or step will be the outboard motor. That box or step I will make pretty, with rounded contours, Teak top, gel coated, etc... The idea is that when in the water the outboard is completely out of sight and unnoticeable. Basically the same platform I currently have but with a step, extended about 8-10 inches long and extended hull with a more flattened profile to promote planning.

 

[willy13]

As a laymen, my definition of a full displacement hull is that it does not have an immersed transom. So I personally would define your hull as a semi-displacement hull, much like many trawlers that will go above hull speed but at a major fuel cost. Personally with auto pilot technology I really do not understand trawlers that use twice the fuel to go an extra 5 knots (just guessing on fuel economy...). But thats me.

 

[gonzo]

For emergency power a 4 to 6HP is all you need.
@willy13 Displacement hulls are not defined by the transom being inmmersed. A double ended Collin Archer type is a displacement hull, in the general use of the word. Planing hulls have rather straigh buttock lines aft, so they lift significantly with speed.

 

[philSweet]

The extension just makes it impossible to clean the rudder and prop. You'll lose more for a fouled prop than you will gain from the extension. The hole is a good idea if it lets you breath better when cleaning the prop, which should be daily in Puerto Rico. The target speed for the Albin should be around 5.5 knots at about 5 hp of shaft power. If your ambitions are for more than that, change boats. An Amel 55 will do 10 knots at full chat. A hunter 50 does a comfortable 8 knots. So you are about 1 million USD worth of boat short of what you want.

 

[Cappuccino]

Update: I've done it and it works!
I extended the hull effectively by 48", added a 20hp 4-Stroke that sits in a hole in the extension and extended the chines. The boat rides leveled, not squating and is much faster. From cruising at 5.5 to 6.5 knots I am now doing 8.5 to 10 knots with head seas and 13 knots with following seas. No drag from the outboard hole, no fouled prop. I have now full control going into reverse (full outboard controls on the helm), a redundancy back up motor and extra speed.

Fabrication time: 35 days to complete it all, including dinghy davits.
Total cost: <sarcasm-on> Just a tad bit much less than the million dollar boat suggested.<sarcasm-off>

 

[Cappuccino]

To the people that helped and gave constructive advise, THANK YOU!!!

To the naysayers, well I'm racking up miles on my new planning A25+4 and wont have time to read toxic nonsence

 

[willy13]

Congratulation on your success!

Did you do a build thread anywhere?