What hp to re-power a 38ft sailboat?

[David97]

I need to re-power a 38ft sailboat (19,200lbs displacement, 10,200lbs ballast, 30ft LWL). A dealer mentioned that a Beta 25hp should be enough to reach hull speed. It seems underpowered. The boat is currently powered with a Westerbeke 4-107. Any view?

[SV_Galateia]

I'm sure you will get varied answers, but I have read that 3 to 4 hp per ton is the norm.

[SVDontpanic]

25hp would probably get you to hull speed in calm conditions, but in any chop or wind your gonna suffer. I've heard the same as SV_Galateia, about 4hp per ton, so for you around 40hp should be good.
My boat is 20ish tons, I have 85hp

[carlosproa]

Originally Posted by David97

I need to re-power a 38ft sailboat (19,200lbs displacement, 10,200lbs ballast, 30ft LWL). A dealer mentioned that a Beta 25hp should be enough to reach hull speed. It seems underpowered. The boat is currently powered with a Westerbeke 4-107. Any view?

Perkins 4-107 is anywhere from 40 to 50HP minus transmission and prop type. 25 HP is small, those high trust engines my do the trick but at a cost of speed. I assuming you are looking for an outboard? Can you reponer with a beta marine? I have my doubts on an outboard when is rough out there and the boat hobby horse. But each hull is different but lots of weight in one end of the boat…

[skipmac]

This doesn't sound like a light weight, performance boat so more HP to get reasonable results.

As noted 25 HP might get you there in a calm but motoring against wind and waves or trying to maneuver in crowded marina in with a current and a cross wind you would be sadly underpowered.

I had a 34' moderate displacement performance cruiser with a 35 hp engine and felt like that was just right. For your boat I wouldn't go any smaller than 40 hp. Max 45-46

[boatpoker]

Our 20,000lb. 38' fantail trawler has a 55hp and we cruise at 7.2 knots in calm water at 1800rpm. We can hit 8.2 knots if we run it up 3200rpm (and triple our fule usage from 0.75gph).

[deblen]

Hull speed in calm conditions doesn't require much power.
Powering into rough seas or current requires much more.
Maneuvering or stopping smartly & safely requires much more plus a substantial propeller.
Around 40 HP IMHO.

[Searles]

I would expect 25 to 35 up to be plenty ,depending on prop dia and pitch ,if plenty of room go for 3/1 gear box ,if you have a feathering prop all the better ,big prop turning slowly is the best way to go ,but not always possible,.⛵️⚓️

[Celestialsailor]

Welcome to the forum David. If you are going cruising, you will experience tides, currents and head winds. 40hp would be my minimum choice. A Beta 38 is you wanted to go that route. But honestly the Perkins 4-107 (40hp) is a great choice. The rebuilds are cheap and parts plentiful. Why not find a good rebuilder and go that route. Probably under $6K. A new Beta 38 would probably put you back around $15K. Plus no engine bed mods.

[Bowdrie]

Your boats size and displacement figures are a bit greater than mine.
I use 40hp, (not a Perkins,) and find it the ticket for being able to back-an-fill with authority, and easily cruise at low rpms with much quieter sound levels.
I'll agree with Celestialsailor, nothing wrong with a Perkins,
The newer rebuilds of 107s/108s are better than the old ones.
Front end drives are better, and most important they don't leak oil, (at least I heard that).

[valhalla360]

What did the manufacturer spec?

Also, how much would you expect to save downgrading from 40hp to 25hp...it won't make any noticeable difference in fuel efficiency.

[Caleb_Grey]

Originally Posted by David97

I need to re-power a 38ft sailboat (19,200lbs displacement, 10,200lbs ballast, 30ft LWL). A dealer mentioned that a Beta 25hp should be enough to reach hull speed. It seems underpowered. The boat is currently powered with a Westerbeke 4-107. Any view?

Would you buy a 38' boat with a 25hp engine? I wouldn't.
Put a beta 60(54hp) in, the next guy will pay for it.

[GordMay]

Greetings and welcome aboard the CF, David.

There’s plenty of opinions, expressed here [including mine, FWIW]:
➥ https://www.cruisersforum.com/forums...ze-1577-2.html

A rough Rule of thumb for determining Horsepower Required for a Sailboat : one horsepower per 500 pounds ( ± 50lbs ) loaded.

Westerbeke Corporation suggests 2 hp for every 1,000 lb of displacement for coastal cruising, and 2.5 hp per 1,000 lb of displacement for offshore. That would mean a 38 ft. sailboat with a displacement of 15,000 lb should have a 30 hp engine for coastal cruising and a 37.5 hp engine for offshore.
In your case: 15 Long Tons = 33600#
Hence: 33. x 2 = 67.2 HP ~or~ 33.6 x 2.5 = 84 HP.

In their book "The Gougeon Brothers on Boat Construction" the authors suggest a good rule-of-thumb is 1 hp for every 500 lb of displacement... that would mean 38 ft. sailboat with a displacement of 15,000 lb should have a 30 hp engine.
In your case 33 x 2 = 66 HP

Some people suggest 1 hp for every ft. of boat waterline length... that would mean a 38 ft sailboat with a waterline length of 30 ft should have a 30 hp engine.
In your case 41 x1 = 41 HP

Some people suggest 3 - 5 hp (continuous rating) per long ton (to calculate the boat's weight in long tons divide the displacement by 2,240)... that would mean a boat with a displacement of 15,000 lb should have a 20 - 33 hp engine. For offshore conditions some people suggest the engine be larger than the size calculated for coastal cruising, possibly + 25%... so in this example the engine size would be increased to 25 - 41 hp respectively.

How do you measure horsepower?
Power is a measurement of the ability to do a unit of work in a specific time. It is calculated, not measured. Horsepower and watts (kilowatts are 1,000s of watts) are units of power. Power is calculated by measuring engine torque at a specific crankshaft rpm and multiplying the 2 figures together.

Engine Horsepower/Torque Formulae

Horsepower = ( Torque in Lb/Ft x Crankshaft Speed in RPM ) ÷ 5252

Power = Torque X RPM
Torque = Power ÷ RPM
RPM = Power ÷ Torque

[MicHughV]

Speaking from hard earned experience...a 25 hp diesel in a 38' boat simply won't cut it.

Sure, you'll move the boat, but not at hull speed.

Engine hp is only one aspect, blade diameter, pitch, number of blades, transmission reduction, etc, etc, all play a part.

You really wanna learn?

Get the " Propellor Handbook" authored by Dave Gerr, will give you every tool you need to determine engine hp.

My suggestion would be nothing less than 40 hp....

[tkeithlu]

To bring up another point, David, installing a different engine in the same compartment can be a nightmare - all the hoses, seacocks, cables, engine mounts, and wiring are in the wrong places even if the compartment space allows for the new engine at all. There are strong reasons to either rebuild the existing engine or replace with an identical engine.

Consensus seems to be that your 40 HP is about right.