Albin 25: Emergency Propulsion/Kicker Motor

Hello to all and happy holidays!
Just like the topic says I am about to convert my 1972 Albin 25' displacement hull trawler from a single diesel trawler to dual power; diesel + outboard trawler. My A25 currently has a Vetus M4.14 32hp diesel with about 400hrs in excellent condition. My plan is to add an 25hp four stroke outboard (143lbs) to the transom of the boat for both emergency and kicker use. The plan also includes adding the controls of the outboard to the helm; electric starter, throttle/gear level, rpms, etc. I also intend to modify the linkage of the rudder and have the outboard also steer with the steering wheel. My A25 currently has a 3ft long custom made fiberglass swimming platform which will be modified in order to adapt the new outboard motor. The plan is to make a hole in the swimming platform in order to pass thru the new outboard shaft thru it. The outboard motor will be in the centerline, not to one side. I am going to extend the platform about 8 inches more (3'-8") and also extend the hull lenght to the new swimming platform's new length. The hole that is going to be made into the swimming platform for the shaft of the outboard to go thru is going to be sealed so that the swimming platform provides extra buoyancy. The aft section of the swimming platform, which in this case would be the end of the hull will be flattened hence converting the displacement hull to semi-displacement, or at least that is my intention. And finally the cowling of the outboard is going to be covered with a custom fiberglass stair cover. The idea is that when the boat is out for the water you will only see the propeller and lower unit of the outboard hanging beneath the swimming platform.
So, after all this is done I should end up with a 27'ish lenght waterline (added speed), a semi-displacement hull (flattened transom), added buoyancy in the aft, with about 57hp in combined power and best of all an emergency power option for when the diesel decides to quit or the propeller decides to catch some debris or ropes floating in the water.
I have some questions or doubts that are still floating in my mind...
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?
I've attached two pictures, one with the current swimming platform and the other with the outboard and extended platform drawn into it.
Thank you in advance and happy holidays

 

Save your money. Get a 6hp saildrive outboard with a big prop. It wont go much faster with the extension and the extra "performance" will be a heavy price.

 

Thanks for the reply and advice!
When you say; "it wont go much faster", the question is how much?
I know is not going to be a lot for the money spent, but any gain in speed would be appreciated.
The boat currently has a speed between 6.5 to 7 knots and that goes with the theorical hull speed. As per hull speed calculations if I extend the hull (water lever length is 23') by let's say 3'-6" the theorical speed would be around 7 to 7.5 knots. Now, how about the extra power? The extra 25hp, assuming I could run the outboard at say 75% wouldn't that account for something extra in terms of speed? 8 to 9 knots maybe, maybe more ☺️???
I know that I am asking a lot but sailing distances here an extra knot that I add accounts for valuable time.

 

+1 re Skaraborg's comments above.

No.
You have a displacement hull and realistically, the maximum speed that you can hope to achieve is probably no more than 7 or 8 knots.
And even 8 knots will require a huge amount of power (relatively, compared to what you currently have), and the fuel consumption will probably double (or triple even) - it is just not worth it.
The boat was designed to potter along happily around 5 - 6 knots while sipping fuel.

If you want to have an emergency source of power, you could consider fitting an auxiliary sailing rig - some Albin 25's were fitted with these by the Builder.
I will attach a copy of a catalogue I have for the Albin 25 - one photo shows the sailing rig.

 

This person is doing 14 knots in a 1970 Albin 25 with a 60hp engine, same hull design as mine but minus the hull extension I intend to do.
Albin Cruisers 25 & 27 Owners | New engine, 3500 tpm,speed 26 km/h | Facebook https://www.facebook.com/share/v/1DzWmDmoMr/
Albin Cruisers 25 & 27 Owners | New engine, 3500 tpm,speed 26 km/h | Facebook https://www.facebook.com/share/v/1DzWmDmoMr/

 

This is the same Albin 25 I mentioned;
Flying Albin, Who Cares | By Bart En Cindy | Facebook https://www.facebook.com/share/v/18QXNXSZKE/Flying Albin, Who Cares | By Bart En Cindy | Facebook https://www.facebook.com/share/v/18QXNXSZKE/

 

Here is another Albin 25 going faster than hull speed. This one is a bit extreme, it has a Ford V8, but it is fast!!!

Albin Cruisers 25 & 27 Owners | Work in procres albin 25 v8 powerd by ford | Facebook https://www.facebook.com/share/v/19ia7a1xB8/Albin Cruisers 25 & 27 Owners | Work in procres albin 25 v8 powerd by ford | Facebook https://www.facebook.com/share/v/19ia7a1xB8/

 

I am not interested in braking any world speed record, just want to add a couple of extra knots when I need them. And like I said before the added power for emergency situations is a plus.
Just wanted to know opinions on the whole setup, the location of the outboard being behind the prop of the diesel, etc... Will it work like a dual prop outdrive? Will it not work? Too much cavitation?? Will I have no problems at all and will work good enough?

 

You have an excellent hull that was designed to excell with around 20hp. It is a displacement hull, so sure, adding to the stern will get you some extra hull speed, but you will be able to do that with the existing engine.

Cutting a hole for a large engine will just induce drag and more likely make performance worse. A lifting or permanent bracket on the aft edge of the platform for a lightweight 6hp motor would be more efficient as an emergency motor and more accessible.

I say this as an observer in Sweden. I have seen more than a few A25 with either old engines being unreliable or even removed, and 6-10hp outboards (usually honda) on transom brackets.

It is of course, your boat, your time and your money. Please report back with your findings.

 

It wont work like a duo-prop.

Build the extension with attention to the buttock lines. Fit the largest Bruntons auto-prop that will fit in the aperture while still having the correct clearance. You will get the optimal speed that the hull and engine can provide.

 

I see a hull squatting into into own stern wave. If you want to put up with the possibly weird handling and all that noise for a few extra knots, go for it.
If time is so important, get a planing boat.

 

I’d address the propeller optimization first, possibly even hot rod the motor a bit. You might see enough gain to skip the hull extension.
That’s a lot of work and expense in return for a maybe.

 

That Albin is a lovely design.
You do not have realistic expectations, it's not gonna work. Please stop.
Make sure what you have is maintained and working correctly or buy what you are trying to create.

 

Thank you all for the opinions!
Answering some of the posts:
I already went thru 3 different propellers with basically zero gain in speed.

The engine is basically new, so hot rodding it for more power I thinks is best just to add an outboard; extra power and when not in use is going to be the emergency power.

Albins 25 are capable of planning given enough power, making a quick search ended up with two different albins "flying" thru the water. One of them has a 60hp engine making 14 knots!! Did any of you saw the videos I attached?
I dont need to go 14 knots, 9 or 10 is perfect. With the 25hp outboard + 33hp Vetus I'll end up with 57hp theorical horses. That is 57 horses, I'm pretty sure the boat can make those 9 or 10 knots I am looking for being that someone else is making 14 knots with 60horses. Obviously this is assuming that the outboard wont cavitate or I am unable to plant all 25 horses from the outboard, hences my original questions in the original post.

The swimming platform is already there, installed working and all. I'll just extend the hull to reach the platform and then some, maybe some 8" inches more. That extension will give extra buoyancy, bouyancy after to where the outboard is going to be placed, I dont see how extra buoyancy in the aft is going to work negatively to make the boat squat. Heck, the Albin with the 60hp making 14 knots doesnt even have trim tabs! The hole for where the shaft of the outboard is going to go thru in the platform is going to be sealed, it will be buoyant, and that same hole will have a plate or something I'll make so that the shaft and platform are seamless, hence almost to no drag.

I have experience working with fiberglass, I made the swimming platform and even the hardtop for the Albin. Making some hull extension in order to get some speed gains and have an emergency motor is nothing I worry about. What I need is someone with experience that could give me some advice regarding the outboard being behind another propeller, in this case a propeller that doesn't have exhaust gases coming out of it. And also some advice in how I should make the hull extension, the end of it; flat, curved??

 

Yeah, i noticed, hence my comment of it sinking into its own trough.

I also notice that despite saying "thanks for the opinions", you are not heeding any of them.

Try googling duo-prop and see what the difference is to what you are suggesting.

Maybe look up "hooked transom" while you are there, maybe some more ideas for your project.